Forty-two Premier League players and staff tested positive for Covid-19 in the past week – the most results ever recorded in the league over a seven-day period.
It is the highest number since 40 cases were reported in January.
That week, 2,295 tests were carried out, while 3,805 tests were done in the latest round from 6-12 December.
Brighton, Tottenham, Leicester, Manchester United, Aston Villa and Norwich have all confirmed cases, with United’s game at Brentford in doubt.
Sunday’s Brighton v Tottenham fixture was postponed following a Covid-19 outbreak at Spurs.
Previously, the most positive tests returned in a week this season was 16 from 16-22 August, when there were 3,060 tests.
The latest report of 42 results is an increase of 30 on the 12 positives reported from 3,154 tests from 29 November – 5 December.
On Thursday, following the introduction of new coronavirus rules in England, the Premier League told clubs to return to emergency measures, including social distancing and wearing masks.
A league statement on Monday said the frequency of lateral flow and PCR tests for players and staff would increase.
The statement added: “We will continue to work closely with the government, local authorities and supporter groups, while being responsive to any future changes to national or local guidance.”
From Wednesday, fans will need to show proof of double vaccination or a negative test to attend sporting events with crowds of more than 10,000 people in England. This includes Premier League games.
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Tottenham’s Europa Conference League match against Rennes was called off on Thursday because of the outbreak that resulted in the Brighton postponement.
Also on Thursday, a number of Leicester players did not travel to Italy for their Europa League group game against Napoli because of positive Covid-19 tests.
United are in discussions with the Premier League over whether it is safe to play their game at Brentford after the club closed their training ground for 24 hours to reduce the risk of transmission.
Aston Villa boss Steven Gerrard confirmed “a couple of staff members and a couple of players” have tested positive but insisted the “vast majority” were negative.
He said Tuesday’s game against Norwich is not in doubt and Canaries boss Dean Smith said one of his players was isolating but the rest of the squad had tested negative on Sunday.
At Brighton, head coach Graham Potter says there are “three or four” positive cases.
In the Championship, Sheffield United’s match against QPR on Monday is off because of an outbreak in the QPR squad.
More to follow.