The Premier League has told its 20 clubs to return to emergency measures in light of new Covid rules in England.
Clubs with high vaccination rates had relaxed some of the measures but must now reimpose restrictions to help limit the spread of the Omicron variant.
Tottenham's Premier League match at Brighton on Sunday has been postponed following a Covid-19 outbreak at Spurs.
A number of Leicester players did not travel to Italy for their Europa League group game against Napoli on Thursday because of positive Covid-19 tests.
The Premier League has not said how many clubs had been able to relax the measures.