The Red Devils saw a small number of positive tests returned among players and staff after they returned from the 1-0 win at Norwich City.

The entire group that travelled to Carrow Road for Sunday's (AEDT) match had tested negative in a round of routine testing.

The individuals who returned positive lateral flow test results on Sunday were sent home before training, which was then adjusted to consist of outdoor individual and non-contact sessions.

The club is understood to have notified the Premier League, with its match against Brentford coming up on Wednesday (AEDT).

Sunday's game between Brighton and Hove Albion and Tottenham was postponed after Spurs suffered a COVID-19 outbreak that also led to their Europa Conference League game with Rennes being called off.

The Championship match between QPR and Sheffield United on Monday has been postponed too, after the London club said they would be unable to fulfil the fixture due to "a number of positive COVID-19 cases within their squad".

The United Kingdom government announced in the past week that fans attending sporting events with crowds of more than 10,000 people will need to provide proof of having had two doses of a coronavirus vaccine or a negative test result.

The change in rules, which is due to come into effect on December 15, is among measures aimed at reducing the spread of the Omicron variant of the virus.

The UK's COVID-19 alert level has also been moved from three to four. Authorities said community transmission of the virus was high and, while mostly driven by the Delta variant, the emergence of Omicron "adds additional and rapidly increasing risk to the public and healthcare services".