Ball seems certain to face FA disciplinary action after referee Rob Styles missed the assault in the second minute of City's 1-0 defeat, which left an ugly scar on Ronaldo's stomach.

At the time, Ferguson launched a furious tirade at the assistant referee closest to the United dug-out.

However, it was only when he got home later on that he fully appreciated what Ball had done.

"They told me at the time the lad had stamped on him but it wasn't until the night time I actually saw what he did," said Ferguson.

"I could not believe it. I don't know what got into him.

"It was the first minute of the game. I don't know if it was instructions, or he was hyped up. It was incredible.

"The game has changed since the 1960s, when there was a lot of really vicious tackling but you don't see that kind of thing nowadays. Cameras are everywhere."

Under such circumstances, it would have been easy for Ronaldo to sidestep the rest of the game.

However, showing the same mental fortitude that allowed him to ignore the terrace taunts which accompanied his return to the Premiership following England's World Cup exit, the PFA and FWA Player of the Year simply bounced back and lured Ball into the challenge from which he netted the matchwinning penalty.

"He wouldn't back down," said Ferguson. "He has shown that kind of courage all the time. The great thing about Cristiano is that he always gets up and wants the ball.

"He reminds me of Celtic's Jimmy Johnstone. He was exactly the same. He would get kicked all over the place but he would just want to attack the big bully who had kicked him to the ground. He would just run straight at them.

"Courage is a quality the greatest players have always had. Pele, Eusebio, Johann Cruyff and George Best always had great courage. That is why they could paint the canvass any way they wanted."

Ronaldo's penalty took him to 23 goals for the season, an incredible return for a winger.

Yet Ferguson, who has seen the Portugal international emerge as one of the world's best players since his arrival from Sporting Lisbon as a teenager, does not believe it is a one-off.

"When he came to us as a young lad, he was hitting double figures all the time," said the Scot.

"For a winger at 18, you are saying that is good. But we always felt he should get more because he got into good positions and just tried to burst the ball by overhitting and the shots were flying over the bar.

"But, as with every young player, he has developed and improved. His finishing is better and his heading ability is underestimated.

"He could get 23 again next season quite easily."

FA disciplinary chiefs will view television footage of the incident during Saturday's Manchester derby and the City defender looks certain to face a charge.

An apparent headbutt by Fulham's Michael Brown on Liverpool's Xabi Alonso will also be investigated tomorrow, it was confirmed today.

An FA spokesman said: "We will look at the television footage of the incidents tomorrow and ask the officials what action they would have taken had they seen the incidents, and any charges will be based on that."

If charges are announced tomorrow, the players will have until Wednesday to respond and under the fast-track system a disciplinary hearing would take place on Thursday.

Officials from the FA's compliance department will also have to decide whether the players should be charged with violent conduct or the more-serious offence of serious foul play.

That was the charge brought against Ben Thatcher earlier this season after his elbow assault on Portsmouth's Pedro Mendes while the defender was playing for Manchester City. He was suspended for eight matches by the FA.