Edinson Cavani may be the subject of an investigation from the Football Association after allegedly using a racially offensive term in a social media post.
The Red Devils were 2-0 down when the Uruguay international came off the bench for the second half and set up Bruno Fernandes to pull one back before heading in two of his own to seal the three points deep in stoppage time.
The 33-year-old shared some of the positive messages he received from fans in the wake of the victory and responded to one post with the message "Gracias n******".
Cavani has since deleted the post.
The FA and United have not commented on the issue as of yet.
Cavani joined the Old Trafford side in a free transfer in October and has scored three goals in five substitute appearances in the Premier League.
Coach Ole Gunnar Solskjaer was full of praise for the striker after his impact in Sunday's game and has been impressed by his movement off the ball.
“He is one of the best because of his experience and qualities, that movement," Solskjaer said.
"He is one of the best movers you can see. He can peel off the shoulder, he can get in front of you, he can pin you.
"He wants to be in between the two posts, which I love. I love a centre-forward who gets in there. It might hurt sometimes but, when you’re there and you get the ball there, you've gambled and the ball’s been delivered, it's a goal. Two goals!”
United captain Harry Maguire went as far as to hail him as an example for other strikers.
"He has been without a club for a few months so he is coming in and catching up. He is a great professional, he is great to have around the place, he is great in the dressing room and I think you saw today what he brings to the club," he said.
"His movement when the ball is wide is to a level that not many strikers can reach. He is always on the move, always getting across people and that’s why he has always scored goals. So if there are any strikers out here wanting to learn and watch, I am sure they are studying his movement and what he has done in his career."