Manager Slaven Bilic, co-owner David Gold and goalkeeper Darren Randolph all felt that Bastian Schweinsteiger fouled the Ireland international as Anthony Martial volleyed the goal that secured a sixth-round replay.
“It was a foul,” said Randolph while Bilic added: “It was obvious, a foul by Schweinsteiger on Randy. I am a bit gutted for that.”
United manager Louis van Gaal disagreed, saying contact was accidental as he argued: “His own defender pushes Schweinsteiger so he did not do it deliberately.”
Bilic was also unhappy that his goalscorer Dimitri Payet was denied a penalty when he tumbled over Marcos Rojo’s challenge in the box.
“Nobody in the world can say there wasn’t a touch,” he added. “There is more than a contact. It is definitely not a dive. It should have been a penalty on Dimitri Payet.
“Rojo slides and when you are sliding in the box and the ball is nowhere near you, you are taking a big gamble and a big risk. It is a penalty.”
Van Gaal, who believed it was not a spot kick, said such moments illustrated why the game needs an official who can watch replays and adjudicate.
“I have said a referee has to decide within seconds and I can see the video,” he added. “That is different. That is why I am in favour of a fourth referee with the video. I have said that already 30 years back.”
Van Gaal praised his players for their powers of recovery as, following defeats to West Bromwich Albion and Liverpool in an exhausting few days, they came from behind to level through Anthony Martial.
“When you can come back from that I think it is amazing spirit in the team in spite of the very nasty week,” he said.
Follow us on Twitter @NatSportUAE
Like us on Facebook at facebook.com/TheNationalSport