Brentford manager Thomas Frank (AFP)
United have reported a small number of positive lateral flow tests within their squad after their win at Norwich on Saturday.
The United players and staff involved were sent home before training on Sunday.
Tottenham had both their Europa League match against Rennes on Thursday and Sunday's Premier League game at Brighton postponed after eight players and five staff members tested positive.
But Frank is hopeful United's visit to west London will still be played as scheduled.
"We are planning to play the game," Frank said on Monday. "That's what we are focusing on. We can't control anything else.
"I think it needs to be a significant amount of Covid cases before the game can be cancelled but to be fair I'm a little bit in doubt when it is enough."
The British government has brought in stricter Covid protocols in response to the spread of the Omicron variant.
But football has still been hit by the virus, with QPR unable to play Monday's Championship game against Sheffield United due to an outbreak in their camp.
Echoing Arsenal manager Mikel Arteta's recent plea, Frank called for clearer guidelines on how many positive tests will trigger a postponement.
"It's a very tricky situation," Frank said. "I think it's very important the Premier League and all of us are following normal society rules and restrictions. That's very important.
"And then if we can make it very clear what the rules are to cancel a game that would be good. But I think all that is just speculation and taking the focus away from what we all want and that is what's happening on the pitch."
Brentford have been hit by Covid themselves, with Ivan Toney and Ethan Pinnock both missing games after testing positive recently.
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