PARIS (AFP) - Uefa has warned teams like Chelsea and Real Madrid that they must "in principle" comply with France's new vaccine passport when the Champions League knockout rounds start next month.

Government sources on Monday (Jan 17) told AFP that all athletes who wish to enter sporting stadia and compete in France will have to be vaccinated against Covid-19.

That has put a major question mark over Novak Djokovic's participation in the French Open, after the tennis world No. 1 was deported from Australia because he is not vaccinated.

And it suggests that European title holders Chelsea must leave any non-vaccinated players behind when they face Lille on March 16 in the last-16 stage, and Real Madrid, who are at Paris Saint-Germain on Feb 15.

"Uefa is liaising with the relevant stakeholders across Europe ahead of the resumption of Uefa's club competitions in February," European football's governing body said in a statement on Thursday.

"The specific conditions under which matches are played in each country are subject to the decisions of the competent authorities in that country.

"Each team will in principle be required to comply with the applicable rules in the country where the match takes place."

The statement went on to note that "the specific competition Annexes - still under elaboration - which contain special rules due to Covid-19 applicable to the knock-out phase, may provide further guidance in this regard".

Another club concerned by the French government's attempt to curb transmission of the virus are FK Qarabag. The Azerbaijani side are at Marseille on Feb 17 on Europa Conference League duty.

In England, the Premier League indicated last month that 16 per cent of players had not received even their first jab.