Chelsea’s unvaccinated players look set to miss next month’s Champions League tie at French club Lille after Uefa updated its Covid-19 rules.
France does not allow unvaccinated people to enter the country.
But it was hoped that Chelsea could move the second leg of their last-16 tie to a neutral venue in order to use their whole squad.
However new rules issued by Uefa on Tuesday now mean that switch will not be possible.
Chelsea will host Lille in the first leg on 22 February with the return leg in France on 16 March.
The club, which is in Abu Dhabi for the Club World Cup, has not disclosed who or how many players are unvaccinated.
Manager Thomas Tuchel, who tested positive for coronavirus on Saturday and is not yet in Abu Dhabi, has previously said: “At some point, everybody who is not vaccinated will face some consequences.
“If players are not allowed to travel to France, this can create problems for us in not being able to use key players.”
Earlier this month, the Premier League said 80% of its players had been double jabbed.