Sergio Aguero, one of the most prolific strikers of his generation, is retiring from football at the age of 33 because of a heart arrhythmia.

“I have decided to stop playing football, it is a very difficult moment,” the tearful forward said. “I decided around 10 days ago after having done everything possible in case there was a chance… but it wasn’t to be. It’s taken me time to digest it.

Doctors initially told Aguero to follow a conservative therapeutic program for three months, but further tests this week determined the issue was severe enough to bring a premature end to his career.

Aguero, who joined Barcelona from Manchester City on a free transfer, suffered from breathing problems while playing in La Liga on Oct. 30. He was hospitalized shortly after and diagnosed Nov. 1.

Aguero played just five times for Barcelona because of a previous calf injury.

A winner of 15 senior titles, Aguero is best remembered for his heroics in the 94th minute of the 2011-12 Premier League season finale, which clinched Manchester City’s first top-flight title since 1968.

He also made his mark at Atletico Madrid and Independiente, won the gold medal at the 2008 Olympic Games, and lifted the Copa America with close friend Lionel Messi last summer.

In all, Aguero scored 427 goals in 786 matches for club and country.

Initially, the prolific striker denied reports that a heart condition had forced him to retire.

“Always positive,” Aguero said Nov. 12. “There are rumors going around, but I’m following the club doctor’s opinion, and we’ll see how I am in 90 days.”

He was substituted and taken to hospital for tests after experiencing dizziness in the first half of a 1-1 draw with Alaves. Aguero motioned to his chest and throat when medics approached him on the pitch.

In January, Aguero tested positive for COVID-19 and required more than a month to recover, disrupting his final season with City. He spent a decade with the club, winning 12 titles and becoming its all-time leading scorer with 260 goals in 390 appearances.

The draw for the last 16 of this season’s Champions League is finally complete, but with the first legs not kicking off until February, a lot could change in the intervening months. Here’s an early breakdown of each matchup, along with predicted outcomes.

Sporting CP vs. Manchester City

• First leg: Feb. 15 at Estadio Jose Alvalade
• Second leg: March 9 at Etihad Stadium

Manchester City are clear favorites to win this game – and among the top three most fancied to win the whole tournament – so why should Sporting CP pose any threat? Even if City don’t sign a striker in January to ease the goal-scoring burden, Pep Guardiola still has a squad deep enough to compete for every trophy.

Sporting have a number of good players, including Pedro Goncalves, who has 11 goals from midfield this season, and Joao Palhinha, a defensive midfielder who’s earning his keep in the Portuguese national team. However, despite Sporting’s relative dominance in Portugal – they’re 12-2-0 in the Primeira Liga this season – they’ve struggled to impose themselves in their first Champions League campaign in four seasons. Given Sporting conceded nine goals in losses to Group C winners Ajax, what on Earth will happen against City’s dynamic core?

Prediction: Manchester City advance 5-2 on aggregate.

Paris Saint-Germain vs. Real Madrid

• First leg: Feb. 15 at Parc des Princes
• Second leg: March 9 at Santiago Bernabeu

This one’s going to go down as the most entertaining tie of the lot. Barring injury, Sergio Ramos will return to Real Madrid for the first time since leaving as a free agent last summer. Kylian Mbappe is a free agent in 2022 and could sign a pre-contract with Madrid in January. Imagine Mbappe playing against his future employers. It’s too much.

But there’s a bigger matter at hand: progressing to the next round. Paris Saint-Germain are quite clearly all in on the Champions League, and an exit at any stage, let alone in the round of 16, would constitute a major failure. You don’t sign Lionel Messi, Gianluigi Donnarumma, Achraf Hakimi, Georginio Wijnaldum, and Ramos in one offseason just to participate in the knockout stage. There’s much more pressure on Mauricio Pochettino to deliver trophies than there is on Carlo Ancelotti, who’s won matches while compensating for injuries to 14 of his players this season. If Karim Benzema can stay healthy, Los Blancos will certainly have a chance to outscore and beat PSG.

Meanwhile, Les Parisiens are yet to blow the competition away despite ample ammunition. Messi has done just fine in the Champions League, scoring five of his six goals for the club in Europe, but his teammates have struggled under the spotlight. Neymar should return in time from ankle ligament damage, but even when the Brazilian has played alongside Mbappe and Messi, PSG have hardly looked like the attacking juggernaut they promised to be.

Prediction: Real Madrid advance 3-2 on aggregate.

Red Bull Salzburg vs. Bayern Munich

• First leg: Feb. 16 at Red Bull Arena
• Second leg: March 8 at Allianz Arena

This matchup seems easy enough for Bayern Munich. Red Bull Salzburg are one of just three teams from outside of Europe’s top five leagues, and they don’t have the same star power as some of the other heavyweights Bayern could have faced, including PSG and Inter Milan.

But there’s more to Salzburg than meets the eye. Runaway leaders in Austria’s Bundesliga, Die Roten Bullen have won 31 top-flight matches in 2021 – more than any team has managed in a single calendar year since the league’s inception in 1974. Their recipe for success includes the same ingredients RB Leipzig incorporated to kick-start their own run up the tiers in Germany: counterpressing, high-energy play, proactive defending, and incredible scouting. Only Chelsea and Leipzig completed more pressing sequences in the Champions League group stage than Salzburg, who conceded just six goals in six games.

Salzburg launched the careers of Sadio Mane, Erling Haaland, and Bayern’s own Dayot Upamecano. Now, they have another star in the making: 19-year-old striker Karim Adeyemi.

Bayern are still favorites, but Salzburg are no pushovers.

Prediction: Bayern Munich advance 4-2 on aggregate.

Inter Milan vs. Liverpool

• First leg: Feb. 16 at Stadio Giuseppe Meazza
• Second leg: March 8 at Anfield

The trip to Anfield will probably be the biggest test of Simone Inzaghi’s coaching career. Last year, Inzaghi took Lazio to the round of 16, only to be embarrassed by Bayern 6-2 on aggregate. While Inzaghi now has a much more talented squad at his disposal, Liverpool are more formidable foes. With 21 goals in 22 matches, Mohamed Salah is playing some of the best football of his career, and the Reds’ Premier League-leading goal differential of 33 shows they’re finding success offensively and defensively.

Inter’s greatest strength is their play down the middle, and as a side that likes to take shots, they should be able to find a way to create chances, even against the likes of Virgil van Dijk. With Lautaro Martinez and Edin Dzeko combining for 21 goals this season, the Nerazzurri can at least go toe-for-toe in the attacking department.

As ever, the battle will be won or lost in midfield. The strength of Jurgen Klopp’s rotation is obvious. Fabinho, Jordan Henderson, Curtis Jones, Naby Keita, Thiago, and Alex Oxlade-Chamberlain are all fit or nearing full fitness, and they should outmuscle Inter’s Marcelo Brozovic and Hakan Calhanoglu. Normally, Inzaghi would place a lot of the ball-winning responsibility on Nicolo Barella, but the Euro 2020 winner will miss at least the first leg through suspension.

Prediction: Liverpool advance 4-2 on aggregate.

Chelsea vs. Lille

• First leg: Feb. 22 at Stamford Bridge
• Second leg: March 16 at Stade Pierre-Mauroy

If the tie kicked off tomorrow, Lille would have a reasonable chance to progress. Chelsea are reeling defensively and manager Thomas Tuchel is dealing with injuries to key players.

However, Tuchel will most certainly find a solution to Chelsea’s current malaise over the next two months. Meanwhile, Lille, facing massive losses from their previous ownership, will have to sell one or two players in January. Sven Botman, who stars in central defense, has already been linked with moves to Newcastle United and AC Milan, and Jonathan Ikone is reportedly on his way to Fiorentina. Midfield lynchpin Renato Sanches is apparently in play as well.

This doesn’t bode well for the reigning Ligue 1 champions. If Romelu Lukaku finds his scoring boots and Timo Werner continues to improve, there’s no reason to think Lille will pull off the upset.

Prediction: Chelsea advance 5-1 on aggregate.

Villarreal vs. Juventus

• First leg: Feb. 22 at Estadio de la Ceramica
• Second leg: March 16 at Allianz Stadium

This is one of the more interesting ties in the round of 16. Neither side is having a great season: Villarreal are in 13th place in La Liga, while Juventus sit sixth in Serie A and trail league leaders Inter by 12 points. Based on name alone, Juventus will be under more pressure to advance. But they’re only slight favorites to win the tie. The Bianconeri also have a tough run of fixtures before the first leg, with matches away to Milan and Atalanta and a daunting home fixture against giant-killers Hellas Verona.

Villarreal shouldn’t enter the round with desperation. After all, it’s their first trip to the Champions League knockout stage since 2016, and there’s no shame in losing to a club like Juventus. The Yellow Submarine is already guaranteed at least €34 million in prize money, plus whatever fraction of TV revenue it manages to generate from this run. That alone would account for more than 30% of the club’s annual turnover.

Things could change if Villarreal lose top scorer Gerard Moreno to injury over the next two months. Alternatively, Juventus could lose a couple of players in the transfer window. One way or another, this one will be tight.

Prediction: Juventus advance 3-2 on aggregate after extra time.

Benfica vs. Ajax

• First leg: Feb. 23 at Estadio da Luz
• Second leg: March 15 at Johan Cruyff Arena

Let’s be honest: Benfica are only one of the last 16 because of Barcelona’s self-sabotage. The Portuguese outfit earned one more point than the beleaguered Catalans while suffering heavy losses to Bayern and dropping points to Dynamo Kyiv, one of the worst sides to play in the group stage this year.

Ajax, on the other hand, demonstrated serious mettle in their first six matches, scoring 20 goals, second only to Bayern. Sebastien Haller accounted for 10 of them, making himself one of just four players in the competition’s history to record double digits through the group stage. Ajax have a whopping plus-45 goal differential in the Eredivisie and thrashed current league leaders PSV 5-0 in October. In other words, don’t expect a battle in the trenches.

Prediction: Ajax advance 6-2 on aggregate.

Atletico Madrid vs. Manchester United

• First leg: Feb. 23 at Wanda Metropolitano
• Second leg: March 15 at Old Trafford

Manchester United must be most relieved with the results of Monday’s redraw. The initial draw pitted Cristiano Ronaldo’s side against Messi’s PSG, and while any contest between the two rivals would excite neutrals, it would harm United’s own chances of progressing.

The Red Devils have a tough but more manageable task facing Atletico Madrid, who barely did enough to reach the knockout round. Their title defense in La Liga has also fallen apart: Sitting 13 points behind leaders Real Madrid, Atletico have been inconsistent at best, having won back-to-back games just twice this season.

Diego Simeone’s men can’t seem to find the right balance between attack and defense: Sometimes they allow three goals in a game, and other times they can’t score at all. They also finished the group stage with a negative goal differential, which is as unexpected as any statistic when it comes to Atletico.

United’s transformation under Ralf Rangnick will require patience. Saturday’s narrow 1-0 win over Norwich City proved there’s still lots of work to do. But United still have Ronaldo. That could be enough, especially in this competition and against this opponent. The 36-year-old recorded 25 goals and nine assists in 35 appearances against Atletico during his time in Madrid.

Prediction: Manchester United advance 4-2 on aggregate.

Marco Asensio followed up Toni Kroos’ beautiful opening goal with a remarkable strike of his own in Tuesday’s Champions League action at the Santiago Bernabeu, as Real Madrid secured top spot in Group D with a 2-0 win over 10-man Inter Milan.

The Spanish midfielder sealed the victory in the 79th minute with a curling strike from outside the box that smashed off the post and into the net.

Real Madrid finished the group stage five points clear of second-place Inter Milan after winning five of six matches.

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