Joey Barton has launched a scathing attack on Wayne Rooney, saying he has failed to reach the levels predicted for him following his arrival at Old Trafford from Everton back in 2004.

Rooney recently signed a new contract at Manchester United, making him one of the highest-paid players in world football, and has been one of the few highlights in what has been a terrible debut season for United manager David Moyes.

But Barton feels that the England striker has failed to become a "world-class" player and doesn't have the mental strength to reach the levels of former team-mate Cristiano Ronaldo.

"Rooney is world class - potentially - but his mentality is the polar opposite to Ronaldo's," Barton said.

Stories of Ronaldo's extra training during his six years in Manchester are well documented.

And former Red Devils power development coach Mike Clegg was more than impressed with the young winger's determination.

Speaking at the start of the year Clegg said: "He had in his mind, 'I need to make myself special and I'm going to have to learn everything I need to become special.

"'I'm going to have to regiment my day and my week, months and years and become as good as I can be by every possible means.' He had a plan."

And Barton feels that it is that kind of determination that is stopping Rooney from becoming one of the world's greatest. "Why is Ronaldo a Ballon d'Or winner and Rooney isn't?" he added. "Players who have worked with both say the level of discipline Ronaldo has is the reason he is where he is.

"When you see Rooney smoking cigarettes is he doing everything he can to be the best player in the world? The gulf is getting wider."

And the former Manchester City player took to Twitter to continue his blistering attack: "I would have to argue that he has not been better since he broke on the scene at Everton. For me that is when he stopped developing."