The Manchester United boss, whose team are battling Chelsea on three fronts this season, described Mourinho's comments about Ronaldo's working class roots as 'below the belt'.

Fergie is a staunch Labour supporter and there are few topics that can cause him greater consternation than derogatory comments about his working class roots.

The row between Mourinho and his compatriot, who last week was named PFA player and young player of the year, began when the Chelsea boss claimed penalties are never awarded against United, something the 22-year-old disputed.

Mourinho then branded Ronaldo a liar and followed that up at the weekend by saying: "Maybe it's about a difficult childhood, no education."

That angered Ferguson, though.

"It is really below the belt to bring class into it.

"I don't know why he has done this. Maybe he is trying to unsettle the boy.

"Just because you come from a poor, working-class background does not mean to say you are not educated.

"What Ronaldo has are principles that is why he has not responded to it. Other people are educated but have no principles."