Manchester City confirmed three more cases of coronavirus on Wednesday, with goalkeeper Scott Carson, teenage midfielder Cole Palmer and a member of staff testing positive.
City were without six other players for their Premier League victory at Chelsea on Sunday following positive tests.
"Manchester City FC can confirm that Scott Carson, Cole Palmer and one member of staff have tested positive for Covid-19," the club said in a statement.
"Both personnel will now observe a period of self-isolation in accordance with Premier League and UK government protocol on quarantine."
With first-choice goalkeeper Ederson one of the other players already isolating, Carson's positive test leaves City short of options for Wednesday's League Cup semi-final against Manchester United.
Zack Steffen is set to play again after featuring at Chelsea.
Ferran Torres, Tommy Doyle and Eric Garcia are the other players also currently isolating while Kyle Walker and Gabriel Jesus, who tested positive on Christmas Day, have now completed their quarantine period.
The Premier League said on Tuesday that 40 players and staff had tested positive for Covid-19 in the latest rounds of testing -- more than double the previous record.
Despite a number of match postponements, rising case numbers and calls from some within the game for a "circuit breaker" to bring infection rates down, the Premier League said it remained confident the season could proceed as planned.