Sir Alex Ferguson vented his fury at Middlesbrough captain Emanuel Pogatetz after the defender's dismissal for a "terrible" tackle on Rodrigo Possebon.
Possebon, 19, was taken to hospital following the challenge in Manchester United's 3-1 Carling Cup win but has not broken his leg as was first feared.
"It was an absolutely terrible tackle," said United manager Ferguson.
"What gets me about challenges like that is that the opponent always claims he has done nothing wrong."
A statement on United's website read: "We can confirm that Rodrigo did not suffer a break to his right leg.
"He was kept in hospital overnight for observation and to assess whether there was any ligament damage to his knee."
Ferguson expressed his disappointment at the reaction of some Middlesbrough officials, who visibly complained as Pogatetz received a straight red card for the foul.
Brazilian Possebon, who was making his first start for United, required six minutes of treatment before play could resume.
"Pogatetz should have just walked off the field," stated Ferguson.
"Then you get their bench screaming that it wasn't a sending off and there is nothing wrong with our player.
"At least Middlesbrough manager Gareth Southgate was very good about it. He apologised and understood the gravity."
606: DEBATE
"We can have no complaints about the decision," he confirmed.
"It is difficult to know why it happened. It was an unusual aberration for him because his discipline has improved in the last two years.
"A couple of lads on our bench did not have the same view as I did but that is dealt with now. We can only hope the lad recovers."
Pogatetz will miss Middlesbrough's next three matches, while Southgate could take additional disciplinary action.
~RS~q~RS~~RS~z~RS~05~RS~)