A United statement read: "Maintaining Covid security is a priority for us. Following routine testing of the first-team training group today, we have identified a small number of suspected positive cases. This has led to those people isolating, pending further tests.

"As a precautionary measure based on Covid protocols, we have taken the difficult decision that we will not now be able to play the friendly match against Preston North End this Saturday.

"We regret the disruption to Preston and disappointment caused to fans. Any Manchester United fans who have purchased tickets for the game will be automatically refunded.

"At this stage, we do not expect further disruption around our forthcoming matches, but we will continue to follow Premier League protocols in this regard."

United are due to close their pre-season programme with a game against Everton at Old Trafford on August 7.