The Premier League has written to its 20 clubs asking them to return training ground protocols to “emergency measures”.
This followed an announcement this week by British Prime Minister Boris Johnson that the government was tightening virus restrictions in England.
The UK has had more than 10 million confirmed cases of coronavirus and more than 146,000 people have died from the virus, one of the highest tolls in Europe.
Rules had been relaxed at Premier League clubs with high vaccination rates, allowing players to remove masks indoors and use their original dressing room.
Clubs have also been advised to limit social interactions, meaning Christmas parties are likely to be off the table.
Tottenham’s Europa League Conference game with Rennes on Thursday was postponed after Spurs reported that eight players and five members of staff had tested positive.
Meanwhile Norwich officials are waiting anxiously for Covid-19 results ahead of the club’s clash with Manchester United. Manager Dean Smith, whose side lost 3-0 to Tottenham last week, faces a nervous wait to find out if any of his players will be ruled out of the United match because of a positive test result.
“We have got a couple of knocks and have got a couple of Covid-related issues that we are waiting on results for this morning,” he told his pre-match press conference on Friday.
“I can’t really let you in on any names, but there’s a couple of players whom we are worried about, so we have tested and we will wait for the PCR results back on them.
“(They are) just feeling a little bit unwell, not likely to be linked to the game last week with Tottenham. It is just in general, I think (like) with the whole nation, (we are) holding our breath at the moment,” he said.
Also, Sunday’s match between Brighton and Tottenham is off as fears rise over the potential impact of the surging Omicron variant on the English top-flight.
As part of the new measures announced this week, fans will have to show proof of vaccination or a negative test to attend sporting events with crowds of more than 10,000 from next Wednesday.
The coronavirus pandemic largely forced football behind closed doors last season but full crowds have returned to English football during the current campaign.