The Premier League found a record 42 cases of COVID-19 among players and staff at various clubs over the past week, it said on Monday just hours after Manchester United's fixture against Brentford was thrown into doubt due to an outbreak at the club.
The 42 positive tests from over 3,800 individuals is more than the tally from the previous seven weeks combined and a record in the English top flight in a single week.
"The League has reverted to its Emergency Measures, and will increase the frequency of both Lateral Flow and PCR COVID-19 testing of players and staff," it said in a statement.
United said they had closed down their training complex following positive COVID-19 tests in the first team.
United are scheduled to play at Brentford on Tuesday but the club said they had approached the Premier League to discuss whether the match should go ahead.
The Old Trafford club did not say how many individuals had tested positive for the novel coronavirus.
"Individuals who tested positive are isolating per Premier League protocols," the club said in a statement.
"Given cancellation of training and disruption to the squad, and with the health of players and staff the priority, the club is in discussion with the Premier League whether it is safe for Tuesday's fixture against Brentford to continue.
"Team and staff travel to London will be deferred pending the result of that discussion."
Aston Villa manager Steven Gerrard and Brighton & Hove Albion coach Graham Potter also said they had players who had tested positive for COVID-19.
"We re-tested this morning and we have got a couple of staff and a couple of players missing for the foreseeable future," Gerrard said.
Potter said Brighton had "three or four" cases. "Now we're just checking and making sure it's at that number."
Last week Tottenham Hotspur had two matches called off due to a COVID-19 outbreak at the club affecting players and staff -- their final Europa Conference League group game against Rennes and the weekend's league trip to Brighton.
While the Brighton game has been postponed, UEFA said the Conference League tie will not be played due to a lack of available days on the calendar, with Spurs risking an exit from the competition if they are forced to forfeit.
Some Premier League clubs could take into account the vaccine status of potential signings when they look to bolster their squads in the January transfer window as rising COVID-19 cases raise fears of a rash of postponed games.
Aston Villa boss Steven Gerrard and his Crystal Palace counterpart Patrick Vieira both said on Tuesday that vaccine status might be a consideration in the decision-making process.
The Premier League announced on Monday it was re-introducing "emergency measures" after a record 42 cases of COVID-19 among players and staff at clubs over the past week, shortly before Manchester United's game at Brentford was called off due to an outbreak at the Old Trafford club.
Gerrard, whose side also have had players and staff test positive this week, told British media on Monday that Villa's thorough recruitment process meant vaccine status could be considered when they speak to potential recruits.
"We look at everything. So I'm sure it will come up," said Gerrard, whose side visit Norwich City later on Tuesday.
"But we'll obviously make decisions as and when we decide a certain person is the one who could come in and make us better.
"But I don't think it's right for me to comment on if I would or wouldn't in that situation. But it would certainly come into conversations in the background."
Palace manager Vieira said clubs needed to find 'solutions' and that the prospect of having a non-vaccinated player missing for 10 days because of COVID-19 isolation rules, could be a consideration in new signings.
"But I don't think that would be the final call on whether to sign a player or not," he told reporters on Tuesday.
England's top-flight is in the midst of its busiest time of the season, with teams involved in the League Cup playing at least twice a week until the first week of January and further cancellations could leave an unwelcome fixture pile-up.
United's match against Brentford was the second to be postponed this season due to COVID-19 after Tottenham Hotspur's game at Brighton & Hove Albion over the weekend was called off.
Tottenham's outbreak meant their UEFA Conference League clash at home to Stade Rennais last week was also called off.
Leicester City, Brighton, Norwich City and Villa have also reported cases as the new Omicron variant takes hold in Britain.
Clubs have been enjoying full stadiums again this season after playing virtually the whole of last term and part of the campaign before that in front of empty or restricted capacity stands following the start of the pandemic in March 2020.
The festive period is traditionally a soccer feast for fans in Britain, with broadcaster Sky Sports trailing its coverage with the slogan "Christmas is for Football".
But rising COVID-19 infections are threatening to put a dampener on the hectic holiday programme, raising fears of a return to restricted attendances or even empty stadiums as seen in Germany and the Netherlands.
From Wednesday, fans will need to show proof of double vaccination under England's "Plan B" of measures to slow the spread of the Omicron variant that are being voted on by legislators on Tuesday.
The Premier League, desperate to avoid a flurry of postponements, has ramped up its COVID-19 requirements for clubs, including daily testing, face coverings to be worn inside and stricter social distancing.
British Prime Minister Boris Johnson has pledged that all adults will be offered a vaccine booster by the end of the month as concerns grow over the spread of Omicron.
Professional football has lagged behind in the take-up of COVOD-19 vaccines, with the Premier League releasing figures in October showing that 68% of its players were double-jabbed.
Addressing the situation in October, England manager Gareth Southgate said some young players were "more open to conspiracy theories" about vaccines.
Mourinho offers jacket to Roma fan who collapsed in stadium
AS Roma coach Jose Mourinho has offered to send his jacket as a get well present to a fan who was hospitalised after collapsing during their Serie A game against Spezia on Monday.
Rome-based newspaper Corriere dello Sport reported that a 23-year-old supporter suffered a cardiac arrest during the first half and was treated with a defibrillator, before being taken to hospital.
Fans in the Curva Sud section of the stadium remained silent for the rest of the game, which ended in a 2-0 victory for Roma.
"I only found out after the game. Of course, we hope everything goes well for him," Mourinho said.
"If it does, he should send in his address and it would be my pleasure to send him my jacket so that he will be wearing it when he next comes here in the cold."
Mourinho's side are sixth in the Serie A standings, 12 points behind leaders Inter Milan.