The Red Devils were in action away to Norwich City on Saturday, recording a 1-0 victory over the Canaries courtesy of a second-half penalty from Cristiano Ronaldo.
According to the Manchester Evening News, the entire squad that travelled to Norwich had initially tested negative for the virus, but 'a small number of players and staff tested positive' on Sunday and were therefore sent home before the training session.
The report claims that some players were able to train at Carrington on Sunday, but the Premier League have been informed, and Tuesday's clash with Brentford is now in doubt.
Man United are yet to release a statement on the situation, and it is unclear which players have returned negative tests.
Tottenham Hotspur's Europa Conference League contest with Rennes was called off last week due to positive cases in the camp, in addition to Sunday's Premier League clash with Brighton & Hove Albion. body check tags ::