The Premier League took the decision to postpone “based on guidance from medical advisors,” said a Manchester United statement issued late Monday.
The decision comes after United became the latest top-flight team to be hit by a coronavirus outbreak, which forced the closure of their Carrington training complex.
The Premier League reported 42 new Covid-19 cases on Monday — a record since testing figures started being released in May 2020.
Also on Monday United halted first-team operations at Carrington for 24 hours after several players and staff tested positive for the virus.
Ralf Rangnick’s squad had not travelled to London.
Aston Villa and Brighton also revealed positive tests on Monday as the virus threatened to wreak havoc on the midweek fixture list.
“Manchester United can confirm that our Premier League fixture at Brentford FC, on Tuesday 14 December at 19:30, has been postponed and will be rescheduled in due course,” a United statement said.
“Following PCR confirmation of positive LFT Covid-19 tests among the first-team staff and players, the outbreak requires ongoing surveillance.
“A decision was taken to close first-team operations at the Carrington Training Complex for 24 hours to help minimise risk of further infection, and individuals who tested positive are isolating in line with Premier League protocols.
“Given cancellation of training and disruption to the squad, and with the health of players and staff the priority, the Club requested the match to be rearranged.
“The Premier League Board took the decision to postpone based on guidance from medical advisors.
“Manchester United regrets the inconvenience caused to Brentford FC and to the fans of both clubs by Covid-19.”
It was reported positive lateral flow tests were returned by a small group of United players and staff on Sunday, with those individuals sent home before the training session began.
With the Omicron variant sweeping across Britain — forcing the government to reintroduce stricter Covid protocols — United’s outbreak comes against a backdrop of growing virus issues at Premier League clubs.
Tottenham’s Premier League fixture against Brighton on Sunday was postponed after an outbreak at the north London club left boss Antonio Conte admitting he and his players were “scared”.
Conte said last Wednesday that eight players and five members of staff had tested positive, forcing the Europa Conference League match against Rennes to be postponed.
Just moments before United’s statement on Monday, Villa manager Steven Gerrard said his team had a virus outbreak, although their game against Norwich on Tuesday is not believed to be in doubt.
Gerrard confirmed “a couple of staff members and a couple of players” had tested positive for Covid-19, which led to Villa cancelling training on Sunday.
However, the squad trained as normal on Monday ahead of their trip to Carrow Road, where United won 1-0 on Saturday prior to their positive tests.
“I made the decision yesterday. On the back of receiving a couple of positive cases, I thought it was just common sense to just cancel the session,” Gerrard said.
“We re-tested this morning and we have got a couple of staff and a couple of players missing for the foreseeable future but the vast majority have come through the test this morning and we look forward to competing against Norwich.”
Brighton manager Graham Potter said there were “three or four” positive tests among his squad, but their match against Wolves on Wednesday is not currently under threat.
The Premier League wrote to all top-flight clubs last Thursday instructing them to reinstate Covid-19 emergency measures, including a return to social distancing and mask wearing.
Arsenal manager Mikel Arteta last week responded to the increase in virus outbreaks by calling for the Premier League to issue clearer guidelines on how many positive tests should trigger a postponement.