Sir Alex Ferguson says he only worked with four players he considered to be world class during his 26 years as manager of Manchester United.

Despite building sides capable of winning two Champions League titles and thirteen Premier League titles during his reign at Old Trafford, he says midfielder Paul Scholes and attacking trio Eric Cantona, Cristiano Ronaldo and Ryan Giggs were the only four that were true world footballing greats.

"They made the difference and the evidence is there," he said.

Ferguson, 73, described Cantona, who United signed from Leeds in November 1992, as "the catalyst", adding "when we brought him in we won the league that season - it was his mere presence and his ability to make and score goals.

"The younger breed like Ryan and Scholes were just fantastic players and the thing about those two was longevity.

"Are there players who have played right through the whole of the Premier League and performed at the level they have? There are none, absolutely none.

"Of course Ronaldo was just a complete genius of a player."

Wayne Rooney, David Beckham, Roy Keane, Carlos Tevez, Rio Ferdinand and Peter Schmeichel all received honourable mentions from Ferguson as "great players", "But these players elevated themselves above all that," he said.

In his new book 'Leading', published today, the managerial legend also reveals that in 2010, he negotiated terms with Manchester United's owners that no player should be paid more than he was.

He recalls: "I told them I did not think it fair that Rooney should earn twice what I made and (joint-chairman) Joel Glazer immediately said: 'I totally agree with you but what should we do?'

"It was simple. We just agreed that no player should be paid more than me.

"We agreed in less time than it takes to read the previous sentence."