Former Real Madrid president Ramon Calderon has claimed that the club will struggle to keep hold of Cristiano Ronaldo if he has asked for a summer exit.

The 32-year-old has reportedly already said goodbye to his teammates and has no intention of reversing his decision to leave, having grown upset by an ongoing tax probe by Spanish authorities.

Only a select few clubs could match Ronaldo's valuation, with Los Blancos unlikely to offload for anything less than £158m, but among those rumoured to be interested is former club Manchester United.

Calderon, who brought Ronaldo to the Bernabeu from United eight years ago for a then-record fee, believes that a reunion could be on the cards if the Portuguese gets his way as he 'loves' the Red Devils.

"I think it is very difficult. 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," Calderon told BBC Sport. "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.

"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 [Sir 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.

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

Ronaldo, who has scored 406 goals in 394 appearances for Madrid, is currently on international duty with Portugal ahead of the Confederations Cup and is said to be "focused and very serious".