Manchester City will launch an internal investigation after Benjamin Mendy appeared to break coronavirus rules by hosting a New Year's Eve party.
City say they are "disappointed" by the incident although felt certain parts of the story had been "misinterpreted" by some sections of the media.
Six players were unavailable for selection ahead of Sunday's Premier League match away at Chelsea - live on Sky Sports - because of an outbreak of positive coronavirus tests within their squad.
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"The club is aware of a New Year's Eve Covid-19 breach involving Benjamin Mendy and the subsequent media reporting of it," City said in a statement.
"While it is understood that elements of this incident have been misinterpreted in the reports, and that the player has publicly apologised for his error, the club is disappointed to learn of the transgression and will be conducting an internal investigation."
Guardiola named Mendy among his substitutes for the clash at Stamford Bridge, despite the left-back's recent coronavirus rule breach.
The City manager explained that Mendy previously had the virus and has recovered from it, and confirmed that he returned a negative swab in the latest round of tests at City.
Guardiola told Sky Sports: "First, the club made a statement. Second, Benjamin already had the Covid so he passed it in the past.
"He has been tested every day like the rest of us and is negative. He explained, he already said it was his nephew and his girlfriend and even friends of his girlfriend were negative too.
"But yes, he knows what he has done and he will learn in the future."
City's last match against Everton was called off due to fears over the virus spreading and all City players were tested twice ahead of the game against Chelsea as a precaution.
However, it is not just at the Etihad where Covid-19 is once again becoming an increasing problem, with Tottenham's fixture at Fulham and Burnley's meeting with Scott Parker's side also postponed, with cases across the league on the rise.
Frank Lampard says there are some players in his Chelsea squad that are struggling with coronavirus for longer than others and admits it has been "very challenging" for his medical staff.
Lampard told Sky Sports it has been a difficult period for himself as well as his club colleagues who are tasked with keeping the players at peak health and fitness.
Asked to describe the situation, he said: "Very challenging, not just for me but the medical team and sports science because some players are asymptomatic and come back training within a few days and reach their top level, but then there are some players who take longer.
"They report tiredness and fatigue and because everything is so new, we don't have anything to gauge it by. We don't have the right methods to know how to get players back to a level as quickly as possible.
"It's not just us but a problem for the league. This year is different and will be different until we get to the other side."
What are the criteria for a postponement?
The Premier League Board ultimately decides whether matches can or can't be postponed. While there aren't hard and fast rules - each game is judged on a case-by-case basis - there are some guidelines.
For instance, in the 2020/21 Premier League handbook, clubs have been told "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."
Teams were permitted earlier this season to name 25 players in their Premier League squad list - and that doesn't include registered U21 players.
Man City, for example, according to the Premier League website, named 20 players in their Premier League squad list. They currently have six players sidelined with coronavirus. That takes their Premier League squad list down to 14.
However, City may not even have had to drop below that 14-player level for their match with Everton to be postponed. The Premier League Board have said they took medical advice into consideration when deciding to call off that fixture, and there may have been other factors affecting their decision.
However, what we do know is that the Premier League Board only rearrange games in "exceptional circumstances".