Pogatetz was instantly red-carded by referee Andre Marriner for his second half tackle on Possebon, the 19-year-old Brazilian who had been impressive up to that point.

The Red Devils went on to win 3-1 but Ferguson was still shaking his head with disbelief after the final whistle.

"The injury looked really bad and the lad has gone to hospital," said the United boss.

"The thing that gets me about challenges like that is that the opponent always claims he has done nothing wrong.

"He (Pogatetz) should have just walked off the field. Then you get their bench screaming that is wasn't a sending-off and there is nothing wrong with our player.

"At least Gareth Southgate was very good about it. He apologised and understood the gravity. It was an absolutely terrible tackle."

Southgate admitted Pogatetz had left Marriner little option than to dismiss him, although the Boro boss insisted his captain had worked hard to clean up a previously dismal disciplinary record.

"We can have no complaints about the decision," admitted the former England star.

"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."

Southgate also confirmed he had tried to placate Ferguson, who had reacted so furiously to the comments from Boro's bench.

"A couple of lads on our bench did not have the same view as I did but that is dealt with now," he said.

"We can only hope the lad recovers."

Southgate is likely to take disciplinary action against Pogatetz, who will be suspended from Boro's next three matches, although Possebon's absence is likely to be far longer.

The 19-year-old was one of the most impressive performers for United, with England Under-19 striker Danny Welbeck also showing up well.

However, it was Ronaldo who grabbed the headlines with his first goal since an equally powerful header in the Champions League final against Chelsea in May.

"Cristiano has done that many times," said Ferguson, who also feels the furore involving Real Madrid has is now well and truly behind him.

"I think Cristiano has come to accept that at this stage of his career, United is the place for him.

"Southern Europeans want at some point to play for Real Madrid or Barcelona, so I understood what was going on in Cristiano's mind when he declared he wanted to join Real.

"But once we had talked he accepted it was a move for the future.

"I pointed out to him how much better it would be to leave like Eric Cantona, with the fans loving and appreciating him.

"The crowd still chant Cantona's name and I told Cristiano 'Leave a hero like Eric' and one day he will. But not yet."

Adam Johnson equalised Ronaldo's header with a powerful second half volley but Pogatetz's departure affected Middlesbrough more than United and the hosts had got on top before Giggs took advantage of Gary O'Neil's slip 11 minutes from time and Nani sealed a place in the fourth round in stoppage time.