Romelu Lukaku is sweating over a possible three-match ban following an incident during Manchester United's 1-0 win over Brighton.
The Belgian striker appeared to twice aim a kick at Seagulls defender Gaetan Bong in the second half of Saturday's match at Old Trafford.
It was missed by referee Neil Swarbrick, but the Football Association are set to review video footage and could take retrospective action.
Should Lukaku be found guilty of violent conduct, he will be banned for United's next three games.
That would rule him out of Tuesday's trip to Watford, as well as the crunch clashes with Arsenal [away] and Manchester City [home].
Lukaku had endured another frustrating afternoon on Saturday as he failed to find the net.
The 24-year-old has mustered just one goal in his last ten matches for United, following an impressive start to life at Old Trafford.
But United boss Jose Mourinho refused to criticised his £75million summer signing, instead praising him for his selfless work.
"In the last minute he was fighting and running back like he was in the first minute, so I think it is also a mentality question," Mourinho said of Lukaku.
"The way Romelu wins the corner for the goal, the way Romelu ends the game making tackles in the left-back position, that is the mentality I want," Mourinho said.
"And, unfortunately, not every player is the same. Players are men, men are different. Men are unique cases.
"Some guys are capable to go into the limits of their efforts and some other guys even with a lot of talent, they don't manage to do that.
"So Romelu, for me, fantastic. Didn't score, I don't care."