The Premier League believes its protocols remain 'robust' after taking medical advice when making the decision to postpone Manchester City's game against Everton.
Everton asked for "full disclosure" of information from the Premier League after the match was postponed four hours before it was due to kick-off at Goodison Park because of a growing Covid-19 outbreak among the City squad.
On Christmas Day, City announced that Gabriel Jesus and Kyle Walker had tested positive, along with two members of club staff. The club have now closed their first-team training ground, which will undergo a deep clean.
It is the second Premier League game this season to be called off due to a coronavirus outbreak, after Aston Villa vs Newcastle earlier this month.
Decisions to rearrange games are only in "exceptional" circumstances and judged on "case-by-case basis", said the Premier League.
Guidance issued to clubs in the Premier League Handbook 2020/21 is that "permission will not be granted to postpone a League match where the applicant club has 14 or more players listed on its squad list available". The final decision is always made by the Premier League Board.
Everton, who would have joined Liverpool at the top of the table with victory, said they would seek clarification from the Premier League as to how the decision to postpone the game was reached given the timing and the fact they were told the game was off rather than consulted as part of the process.
"Everton Football Club regret the postponement of tonight's match against Manchester City - not only for the 2,000 fans who would have been attending, but for supporters on Merseyside and across the world," a club statement read.
"Our players were prepared for the game, as were both the team staff and everyone at Goodison. Matchday is the most important date in our calendar. And this was a big one.
"Whilst Everton will always have public safety uppermost, we will be requesting full disclosure of all the information that Manchester City provided to the Premier League, so the club can be clear on why this decision was taken."
Manchester City are next due in action away at Chelsea on Sunday, before playing Manchester United in the semi-finals of the Carabao Cup on Wednesday January 6. They beat Newcastle 2-0 on Boxing Day.
Would City have to forfeit to United?
Three months ago Leyton Orient had to forfeit their game against Tottenham in the third round of the EFL Cup, but this will not be the case for Manchester City who are due to play Manchester United in the semi-finals.
The rules in the competition changed from the fourth round, meaning games are no longer forfeited, as long as they are rearranged at the earliest reasonable opportunity. So the two Manchester clubs will just have their fixture postponed to a later date.
A Manchester City statement read: "After the latest round of Covid-19 testing, the club returned a number of positive cases, in addition to the four already reported on Christmas Day.
"With the security of the bubble compromised, there posed a risk that the virus could spread further amongst the squad, the staff and potentially beyond.
"Based on strong medical advice the Premier League, in consultation with both clubs, have decided to postpone the fixture.
"All positive cases involving players and staff will observe a period of self-isolation in accordance with Premier League and UK Government protocol on quarantine. The first team training ground at City Football Academy will close for an indeterminate period, with the squad and associated bubble undergoing testing before any decision is made for training to resume.
"Everyone at the club wishes all of our colleagues a speedy recovery ahead of their return to work, training and competition."
Manchester City's players will be tested for Covid-19 again on Tuesday, and the results of the testing will determine whether it is possible for the Chelsea fixture to go ahead.
There is a belief at City that the outbreak has emanated from their trip to London for their Carabao Cup quarter-final against Arsenal on December 22, although no blame is being attached to the Gunners.
London was placed into Tier 4 coronavirus restriction on Sunday December 20 after a new, more infectious strain of coronavirus was found to be driving increased infection numbers in London and the South East.
The UK government has no talks planned on pausing elite sport in England and a review of the new Tier system in England is expected to take place on Wednesday.
A Premier League statement released on Monday afternoon read: "Manchester City lodged a request with the Premier League today to rearrange the game following an increase in positive Covid-19 test results received by the club this morning, on top of the cases reported on Christmas Day.
"This rise has created uncertainty and the Premier League Board received medical advice that the match should be postponed. The Board agreed to rearrange the game as a precaution, and further testing will now take place Tuesday.
"The decision has been taken with the health of players and staff the priority. The Premier League continues to have full confidence in its protocols and rules, and the way in which all clubs are implementing them.
"The League wishes those with COVID-19 a safe and speedy recovery and will rearrange the postponed fixture against Everton in due course."
Analysis: Chelsea game unlikely to go ahead
Sky Sports News reporter Ben Ransom:
"Today is going to be about trying to see if Manchester City can find out exactly how widespread this latest outbreak is. The players will be coming to the training ground to get tested today, the training ground itself has been closed for an indefinite period.
"Obviously, there is a fear that it's going to be even more widespread, and if the players are coming into contact with each other - which is only natural with their training and matchday preparations - that the virus can spread right through the team even further.
"That Chelsea game at the moment looks pretty unlikely [to go ahead], given our experience of what we've seen with other teams in the Premier League and most notably what happened with Newcastle and the length of time that they've had to have their squad in isolation.
"Clearly this is a significant outbreak - otherwise City or the Premier League wouldn't have taken action that happened yesterday in postponing the game."
EFL and National League hit by Covid
Doncaster's next three League One games have been suspended, Rochdale and Morecambe announced that their next two games were postponed, while five games were unable to take place in the fifth-tier National League on Monday.
Rochdale's next two League One games, at home to Crewe on Tuesday and Saturday's visit of MK Dons, are off with players and staff from the hosts forced to self-isolate.
League Two Morecambe were due to play at Bolton on December 29 and away to Bradford on January 2.
National League games at Barnet, Boreham Wood, Chesterfield, Dagenham & Redbridge and Sutton were postponed on Monday after positive tests were returned at various clubs.
Rotherham's Championship game with Barnsley on Tuesday will go ahead, but boss Paul Warne said the coronavirus-hit Millers are only fulfilling the fixture to avoid receiving a possible points deduction.
The EFL remains confident it can cope with the increasing number of games that are having to be postponed because of coronavirus cases.