Real Madrid and Chelsea face the prospect of leaving unvaccinated players at home for the away legs of their upcoming Champions League last-16 matchups due to a law change in France.

France’s parliament passed a law Sunday that mandated proof of vaccination or a recent COVID-19 recovery to enter sports venues and other public places in the country. The new ruling is set to come into effect Monday.

Real Madrid travel to Paris Saint-Germain on Feb. 15 for the first leg of their last-16 clash. Chelsea take on Lille in the same round of the competition, with the game in France scheduled for March 16.

“UEFA is liaising with the relevant stakeholders across Europe ahead of the resumption of UEFA’s club competitions in February,” UEFA told ESPN’s James Olley in a statement on Thursday.

UEFA said clubs would have to adhere to the rules in each country. However, European football’s governing body revealed it’s exploring the possibility of exemptions for players competing in the Champions League, Europa League, and Europa Conference League.

“Each team will in principle be required to comply with the applicable rules in the country where the match takes place,” UEFA added, “but the specific competition Annexes – still under elaboration – which contain special rules due to COVID-19 applicable to the knockout phase, may provide further guidance in this regard.”

UEFA’s guidelines indicate there’s a chance both legs of the round-of-16 ties will be played in a neutral country, Olley reports.