The midfielder limped out of United’s Uefa Europa League win against Partizan Belgrade after being caught by a late tackle.
Harry Maguire, who also appeared to pick up a knock but managed to complete the 90 minutes, is expected to be fit, however.
”Scott is more of a concern, so let’s see how he recovers in the next few days.
“He said he was going to be okay out on the pitch and he said ‘I’ll be fine’.
“He’s tough, but he had to come off. But I hope he’ll recover for Sunday, but I don’t know.
“Inside of his ankle. I think he went over on his ankle.”
McTominay has established himself as a key figure in midfield this season, particularly in the absence of the injured Paul Pogba.
He has forged a partnership with Fred in central midfield, with the pair helping United to a four-game unbeaten run before last weekend’s set back at Bournemouth.
Graham Potter’s Brighton visit Old Trafford two points ahead of their opponents, and will be seeking a third consecutive Premier League win.
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