The striker was dismissed just seconds into the second-half of Saturday's dramatic draw at the Liberty Stadium which saw Chris Morgan cancel out Jason Scotland's penalty three minutes from time.

Referee Andre Marriner ordered Henderson, a £2m summer signing from Watford, back to the dressing room after ruling he caught Angel Rangel with an arm as they contested an aerial ball.

Sam Ellis, United's assistant manager, refused to criticise Marriner – "They have a hard enough job as it is and we're not going to make it any harder" – but did confirm that officials at Bramall Lane could ask the Football Association to overturn the decision if replays suggest Henderson was hard done by.

Speaking immediately after the match, which saw United slip to seventh in the table, Ellis said: "We've yet to view the video. We'll decide what to do when we have.

"We're not going to have a go at the ref. He sees something and he gives it. We'll have to have a look at it first."

Henderson found an unlikely ally in Swansea manager Roberto Martinez who claimed he had not deliberately set out to cause his fellow Spaniard harm.

Martinez said: "It can be hard because, if you go with your arm and the referee sees it, then you go

"It's hard because it happens even if there's no malice in it and I don't think he (Henderson] had any malice."

United were indebted to goalkeeper Paddy Kenny for five saves as they battled to overcome their numerical disadvantage.

Marriner also found himself at the centre of controversy when, in the 55th minute, he awarded Swansea a spot-kick after Gary Naysmith's tackle on Darren Pratley despite United's claims the offence had taken place outside of the area.

Ellis said: "It was contentious. Some people are saying it took place outside of the box but it was an injudicious challenge and we should have dealt with it better."