Real Madrid will struggle to change Cristiano Ronaldo's mind if he wants to leave and Manchester United is a possible destination for the forward, according to Ramon Calderon.

Two weeks after helping Madrid to retain their Champions League crown, Madrid were rocked on Friday when reports in Portugal – since backed up to other outlets by sources close to the 32-year-old – claimed he no longer wants to play in Spain amid scrutiny over his tax affairs.

Ronaldo's representatives have strongly denied an accusation that the forward concealed earnings and defrauded the Spanish tax authorities out of €14.7million.

Madrid have expressed "full confidence" in Ronaldo and believe he will be proven innocent of any wrongdoing, but nonetheless the Portugal international is claimed to have made an "irreversible decision" to leave Santiago Bernabeu.

Despite Ronaldo's relationship with Old Trafford boss Jose Mourinho not being perfect during his compatriot's three years in charge at Madrid, former Bernabeu president Calderon believes a reunion could be on the cards.

"I think it is very difficult [to change his mind], Calderon said to BBC Sport. 

"I had the same situation with Manchester United when he wanted to leave and I signed him. He said, 'I want to leave' and that was that.

"The same year I had the problem with Robinho and he wanted to leave. As a president you can't do anything other than let him go and get the best deal possible.

"I hope he hasn't decided to leave but if he has already made his mind up, it will be difficult to change the situation.

"Very few clubs can meet his expectations. Not because they can't pay the money but because they need to offer him the possibility of winning titles and personal awards."

On Mourinho, Calderon added: "The relationship in Madrid wasn't the best but that doesn't mean he doesn't want to go back to Manchester where he is very grateful of what happened.

"He delayed his move to Madrid for a year because Alex Ferguson was like a father to him. He loved the club, the fans, the city and I don't rule out a move back."

As well as return to United, Ronaldo has been linked with Paris Saint-Germain and Calderon thinks a lucrative move outside of Europe is not an option at this stage of his career.

"I am sure he will stay in Europe," he said.

"I don't see him playing in China or the Middle East. He is not that type of player. He has three or four more years to be a top, top player and he would like to keep winning titles, anywhere he goes."