Mainoo limped out of the 3-0 home defeat to Tottenham, seconds after skipper Bruno Fernandes was sent off towards the end of the first half, with Mount taking his place.
However, our no.7 then sustained a nasty-looking head injury after a forceful aerial challenge from Spurs substitute Radu Dragusin and was escorted down the tunnel, with Amad entering the fray for the closing five minutes plus stoppage-time.
With Fernandes facing a three-match domestic ban, starting after Thursday's game against Porto in his homeland, the Reds will hope for good news on his fellow midfielders.
"I can't say in this moment," Ten Hag told MUTV's Liam Bradford after the game at Old Trafford.