Manchester City reserve goalkeeper Scott Carson, midfielder Cole Palmer and a member of staff have tested positive for COVID-19, the Premier League club said on Wednesday.
The result came in hours before their League Cup semi-final at Manchester United.
The trio join a growing list of individuals who have contracted the disease at the club.
Manchester City missed six players due to positive tests in their 3-1 league victory against Chelsea last weekend.
The club said in a statement that they would observe a period of self-isolation in accordance with league and UK Government protocols on quarantine.
Manchester City’s game at Everton last week was also postponed due to several positive cases in their camp.
The Manchester club have joined Newcastle United, Sheffield United and Fulham among those who have suffered virus outbreaks.
The Premier League returned 40 new COVID-19 cases on Tuesday, the highest in a week this season, after two rounds of testing last week.