Former Manchester United defender Rio Ferdinand has responded to Sir Alex Ferguson's claim that he only managed four world-class players during his time at the club, questioning the Scot's definition of the term.

Ferguson named Ryan Giggs, Eric Cantona, Paul Scholes and Cristiano Ronaldo as the four deserving of the label in his new book, despite the wealth of talent that the ex-manager had at his disposal during his 26-year tenure at Old Trafford.

On his personal Facebook page, Ferdinand challenged his former boss over what qualifies a player to be called "world class".

"What equates to being world class?" he wrote. "Sir Alex Ferguson named four players from his time at MUFC as being 'world-class' (where was mine among a few other names boss!!)

"How does he judge a player to be world class? Performing in the big games, consistency, a high level of ability in all areas of the game, great goalscorer, great saves, great tackler, influential leader, match-winning contributor.

"That list could go on and on with many different areas to judge upon! There is no common rule that serves up the criteria. I do believe that a world-class player must be someone who could walk into any team in the world and improve them. Of course the Ronaldos, Peles, Maradonas, Cruyffs, Messis and Cristiano Ronaldos would all do that no problem..."

Ferdinand was signed by Ferguson from Leeds United in 2002 for around £30m, then a British record, and he went on to make 455 appearances for the club in all competitions over 12 seasons.