Manchester United forward Wayne Rooney lacks the mentality to become a "world-class" player, says Queens Park Rangers midfielder Joey Barton. But Barton - an admirer of Rooney - said his mental approach leaves him behind the world's best on the pitch.

"Look at his approach and mentality compared to Cristiano Ronaldo's. Polar opposites," he told BBC Radio 5 live.

The 31-year-old added: "Rooney potentially, could have been world class. But why is Ronaldo a Ballon d'Or winner and Rooney isn't?

"Players who have worked with both say the level of discipline Ronaldo has is the reason he is the best player in the world."

Barton stressed that although he considers Rooney to be "the epitome of a class Englishman", he feels players such as Real Madrid forward Ronaldo are more deserving of the 'world class' label.

"When you see Rooney smoking cigarettes," Barton continued, "is he doing everything he can to be the best player in the world? The gulf is getting wider but if it was on talent alone, Rooney is a better player than him."

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