Speculation that Cristiano Ronaldo could be set for a sensational return to Manchester United has been given weight after former Real Madrid president Ramon Calderon claimed the forward was "fed up".

The Portugal international has recently been making noises that he is not fully content at the Bernabeu. It's a situation thought to stem from slipping behind the highest-paid earners in football, with Radamel Falcao and former Manchester United team-mate Wayne Rooney understood to be among those earning more than the Ballon d'Or holder.

In a recent interview, Ronaldo himself hinted at a possible return to Old Trafford: "I love Manchester," he said.

"Everyone knows that — I have said it many times. Manchester is in my heart. I left many good friends there, the supporters are amazing and I wish I can come back one day."

Comments today from Calderon will only rock the Bernabeu boat further after he claimed that Ronaldo's relationship with Florentino Pérez, the current Real Madrid president, is unstable.

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“My impression is he is fed up with the policy of the current president,” Calderon told Alan Brazil Sports Breakfast on TalkSPORT.

“When he came [to Real Madrid] with [Arjen] Robben he thought he would be a good colleague for him in the team [but then he was sold].

“Two years ago it was [Gonzalo] Higuain sold and he didn’t like that. Last year he thought it was a mistake to let [Mesut] Ozil leave and the last straw was selling Xabi Alonso and Angel di Maria this summer.”

Should Real Madrid sell Ronaldo, Manchester United would have first option on him and according to Calderon a return to Old Trafford would appeal to the player.

“When I signed him in 2008, I remember he said he was grateful to Manchester United. He had a marvellous time there, he likes everything. It is a really great club."