Sir Alex explained why Wayne Rooney was wrong to quit Man Utd

Alex Ferguson took a leaf right out of Eric Cantona's book as he explained why Wayne Rooney was wrong to quit Manchester United.

United legend Cantona is famous for his seagulls and trawlers speech - and Fergie's oration last night may go down in history the same way.

He compared Rooney's decision to cows in different fields, implying that the grass is not always greener elsewhere.

Ferguson said after the 1-0 Champions League victory over Bursaspor: "Sometimes you look in a field and you see a cow and you think it's a better cow than the one you've got in the field.

"It's a fact, right, and it never really works out that way. It's probably the same cow and it's not as good as your own cow. Some players like to think there's a better world somewhere else. It never really works."

Ferguson insisted it was hard for any club to produce success over a longer period than four years at a time and that Rooney should understand that.

He also made it clear he knew perfectly well that the old stagers like Ryan Giggs, Paul Scholes, and Gary Neville would have to be replaced - which is why he was investing in youth.

United's boss added: "To maintain success at any football club is not a certainty.

"I always believe a four-year cycle is probably the most you can achieve. There are very, very few teams who can create more than a four-year cycle.

"Last season we almost did it. We were one point short of winning the league.

"We have been doing this for the last three or four years and we realised that to maintain the high consistency of being there, which is as important as anything, we had to inject youth into the club.

"We realised a few years ago that Giggs, Scholes and Neville were never going to last for ever and so our policy is to develop footballers in their place.

"I had a player once who said to me that Rooney and Ronaldo weren't good enough and he was not prepared to wait until they were good enough.

"But that's the trouble with potential. People don't identify potential. They're very poor at it.

"I've identified all my life the potential in young people. I know potential. I know how to develop and have faith in it. And young people surprise you when given the opportunity. That's what this club is all about.

"When you see Manchester United at the moment with all these young players, 14 aged under 22, you can't see Manchester United three years ahead."

Ferguson maintained that money would be there if he needed it to make a marquee signing and that if David Villa had wanted to come to England, United would have been right in the mix for him.

He declared: "We will invest for signature players when the time is ready but this summer was not right for me.

"There was one player, yes, we would have liked to have got and he chose another club. I don't think he wanted to come to England.

"Some players don't want to leave their country and it's a fact of life. If they don't want to leave, we just forget about it.

"In terms of Manchester United, there are a lot of things - history, respect. If I told you how agents call me every week and say their player would love to play for us.

"I'm not just talking about run-of-the-mill players. I'm talking about players at almost every club in the world.

"It's amazing, because we've still got that fantastic romance.

"It's difficult to maintain a cycle of more than four years at a time. At the end of the day, we lost a fourth successive title by a point. It would have been a record. We don't like that and we'll try to do something about that. But we'll be there.

We'll be OK. I have every confidence in that.

"We have a structure at the club which is good.

"We've the right staff, the right manager, the right chief executive, who is a brilliant man.

"There's not a thing wrong with Manchester United, not a thing wrong with it. I've only won 27 trophies.

"We don't want this to carry on. We don't want it to become a saga. We've important issues, a team to consider.