Lukaku was caught on camera lashing out backwards at Bong twice, after the ball had been cleared from a corner.
The referee missed the incident at Old Trafford, which happened shortly before Ashley Young’s shot was deflected in by Lewis Dunk, for the only goal of the encounter.
If the FA decide to charge the Belgian striker, he would likely be banned for three games; United’s trip to Watford on Tuesday, their visit to Arsenal on Saturday and the Derby against Manchester City eight days later.
Meanwhile, manager Jose Mourinho has praised Lukaku’s work ethic and slammed United players who can’t match it.
“In the last minute he was fighting and running back like he was in the first minute.
“The way Romelu wins the corner for the goal, the way he ends the game making tackles in the left-back position, that’s the mentality I want.
“Unfortunately, not every player is the same. Some are capable of going to the limit of their efforts but others, even with a lot of talent, are not able to,” Mourinho said.