And he suggested that the Spanish champions may retire the number altogether when their captain ends his playing days.

"We don't know if he (Ronaldo) will come, but he won't take the number away from Raul. That is untouchable, whoever comes," he told Marca.

"I would like to retire Raul's number, like they do in basketball.

"In other sports, a legendary player keeps his number for ever and nobody else uses it."

And Calderon believes Real should already have retired the number nine shirt a long time ago in honour of the great Alfredo Di Stefano.

"I believe Di Stefano's number nine shirt should have been kept back," he added.

"It wasn't done, but I would like to do it with Raul and take advantage to also include Juanito (a former Real and Spain striker who tragically died in a car accident in 1992 at the age of 37, and also wore the number seven at the club).

"It would be shared. To not do it would be to forget players who have given much to this club.

"It would be a nice thing to retire the shirt and keep it in the club's museum."

AC Milan have retired the number six shirt worn by legendary defender Franco Baresi and will do the same when their captain Paolo Maldini - who wears the number three - retires.

Ajax, meanwhile, last year retired the number 14 shirt worn by Johan Cruyff to commemorate their former idol's 60th birthday.