Former Real Madrid president Ramon Calderon has told ESPN FC that he believes both Cristiano Ronaldo and Gareth Bale could leave the Bernabeu in the summer.

The duo have been heavily linked with Manchester United in recent months, with United reportedly having had offers for Bale rejected in last summer's transfer window.

On Thursday, Spanish newspaper Marca suggested Bale's advisers had opened talks with Real Madrid over a new contract -- but that claim has been denied by his agent, Jonathan Barnett.

Meanwhile, Ronaldo has remained coy about his future plans, with rumours that he could be preparing to join Paris Saint-Germain or return to his former club Manchester United continuing.

Calderon, who was president between 2006 and 2009, said: "I get the impression that everything is possible for Ronaldo and Bale.

"Both players have said nothing about what they will do at the end of this season, and that is because they want to wait and see what is happening at Real Madrid.

"The top players in the world always have the option to move to Manchester City or United, to Paris Saint-Germain, to Bayern Munich, maybe Chelsea as well. These are the only clubs that could sign Ronaldo or Bale.

"United, clearly, are interested in signing both players and while it would be hard to do a deal to sign Ronaldo and Bale in the same summer, it is very possible that one could move to Manchester United. Of course this is possible."

Cristiano Ronaldo (R) applauds next to Gareth Bale during a training session at the Valdebebas training ground in Madrid on December 4, 2015. Photo: AFP

Calderon said he suspected Ronaldo and Bale would seek assurances that they will remain key players in the Real team before committing their futures to the club.

"Ronaldo is always keen to get personal recognition for what he has given to Real Madrid," he added.

"It is important that the club show their respect to him because we all know what he has given since we signed him from Manchester [United] in 2009.

"Bale's position is now stable after a difficult season last time, and I believe the fans are supporting him again. He has been playing well, with his ongoing injury problems the only concern at this moment.

"The way Real Madrid is run, it's always to be decided in the summer what happens next. This is true of the coach and the players. For Ronaldo and Bale, it is no different."

Calderon suggested the position of the head coach at Real Madrid could be crucial in deciding the future of Ronaldo and Bale, with Zinedine Zidane needing to make a mark to remain in position for the long term.

"Players like Ronaldo and Bale want to be at a club with a good plan, to be comfortable in their position in the team and to win trophies," he said.

"If they believe that can happen with Real Madrid next season, maybe Ronaldo and Bale will decide it is best for them to stay.

"If not, the club will change direction again and the players will also change. This is the way at Real Madrid."