Manchester United cancelled training and shut down first-team operations at their Carrington headquarters as the club battled to contain a Covid outbreak.
Their fixture at Brentford on Tuesday is hanging in the balance after United asked the Premier League to postpone it.
A number of players and staff were sent home before training on Sunday after testing positive, and Monday's session was scrapped to limit the risk of further infections amid concerns over the spread of the Omicron variant.
Manchester United have been forced to shut down first-team operations at Carrington
United closed down first-team operations for 24 hours, although the academy and women's team continued as normal because their players are in separate secure bubbles.