Bruno Fernandes was spotted appearing to share a laugh with Michail Antonio at the expense of team-mate Paul Pogba.
Pogba gave away a penalty for handball as he attempted to get out the way of a fierce Declan Rice shot just before half-time.
It initially appeared Pogba had been hit in the face as he went down, only for VAR to confirm it had hit his raised arms as Antonio made no mistake to convert from 12 yards.
As the teams returned to the pitch for the second half, the West Ham attacker looked to be imitating Pogba's handball as he spoke to Fernandes and the pair shared a laugh over the incident.
Pogba could be seen looking on in the background and appeared far from impressed as he attempted to focus on a big second half.
Mason Greenwood eventually netted an equaliser for United, but they dropped two points in the top four race as a result of Pogba's error.
And club legend Gary Neville was scathing in his criticism of the Frenchman as he watched on co-commentary duty on Sky Sports.
Watching the first replay, he said: "He's in trouble. He's in big trouble, Paul Pogba.
"He's in big, big trouble. He's given a penalty away then pretended it's hit his head."
He continued to slam the Frenchman as VAR looked at the footage.
"It's rubbish from him. Rubbish," he blasted.
"And to think I felt a little bit sorry for him. I thought he took a whack in the head. Embarrassing.
"I don't know why VAR are looking at it that long to be honest, it's a penalty.
"He shakes his head. Is he trying to make out he's got a bloody nose?
"No brainer, don't know what he's looking at, it's a penalty.
“I could say less if it was instinctive, but that ball was 15 metres away.
“I don’t know why they’re looking at it so long, VAR, it’s a clear penalty.
“You don’t do that, you take it in your grid."
As the second half started, he added: "There's no case."
