Manchester City boss Pep Guardiola has tested positive for Covid-19 among a major outbreak at the Premier League leaders affecting 21 players and staff, while Burnley manager Sean Dyche has also been sidelined by the virus.
However, all 32 FA Cup third-round ties set for this weekend, including City's trip to League Two Swindon on Friday, are still set to go ahead.
"The City manager recorded a positive test on Tuesday along with assistant Juanma Lillo. Both are now isolating, along with a number of other positive cases within the City first-team bubble," City said in a statement.
"This brings the number of those isolating for Covid-related reasons amongst the group to 21. Of that number, 14 are backroom staff and seven are first-team players."
Another of Guardiola's assistants, Rodolfo Borrell, is set to take charge of the English champions.
"He has got the virus but fortunately he doesn't have a lot of symptoms," Borrell said of Guardiola's health on Thursday.
"We have to prepare for the game to happen. If tomorrow it is not possible because of more news, this is out of our reach for now.
"Possibly, (it will) be one of the most easy line-ups we have to decide. We just play with the ones available. We don't have much more."
The Omicron variant of coronavirus has resulted in record case numbers across Britain, forcing the postponement of many matches over the past month.
City are one of the few clubs not to have had a match called off yet and they have amassed a 10-point lead at the top of the Premier League.
The first leg of Liverpool's League Cup semi-final against Arsenal, which had been due to take place on Thursday, was rescheduled after an outbreak forced Liverpool to close their training ground.
Dyche will miss Burnley's tie against Huddersfield after he tested positive on Tuesday, the club said in a statement.
The Premier League announced on Monday that 94 positive cases were detected on 14,250 tests carried out on players and staff between December 27 and January 2.
It was the first week-by-week decrease in positive tests since early November, with a record 103 positives recorded the previous week.