The Premier League has told its 20 clubs to return to emergency measures in light of new Covid rules in England.
The protocols, which include social distancing, were brought in at the start of the season.
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.
The protocols also include wearing masks in indoor areas, therapy taking no longer than 15 minutes and medical staff required to be wearing full PPE when in contact with players.
Tottenham’s Europa Conference League match against Rennes on Thursday was also called off after eight players and five members of staff tested positive for coronavirus at the London club.
Spurs were forced to close their first-team training centre on Wednesday.
Prime Minister Boris Johnson announced the government was introducing ‘Plan B’ to fight the spread of Omicron on Wednesday.
The new rules include making it mandatory for fans to show proof of double vaccination or a negative test to attend sporting events with crowds of more than 10,000 people in England.
All Premier League clubs will have to comply with this measure from Wednesday.