Get the latest United transfer window updates, pre-season news and analysis delivered straight to your inbox every day for free Manchester United received up to nine positive cases from lateral flow tests at their Carrington training complex on Thursday.
It is understood up to five players and four staff members returned positive tests that were carried out at Carrington on Thursday.
United are awaiting the results of PCR tests for the players and staff members who tested positive but have cancelled their scheduled friendly at Preston North End on Saturday.
Manager Ole Gunnar Solskjaer's coaching staff was forced to isolate in February following a positive case and, although United have previously had isolated cases of Covid-19 on the