Ronaldo will have a minor operation on his knee on Saturday and will be ready to return to training with Real Madrid on July 27, Brazil's team doctor Jose Luiz Runco said.

"Ronaldo's injury is like having a stone in your shoe. Sometimes it hurts and other times it doesn't, but it always comes back to annoy you," Runco told Saturday's Spanish sports daily AS.

Runco has said the player, who wanted the operation, was suffering from tibial calcification around the tendon in his knee and needed surgery to remove the calcium.

The operation will take place in Brazil with a Real doctor in attendance.

"We can remove the calcium without damaging the tendon, though once an operation gets underway anything can happen," Runco added.

"I think he will be able to start the pre-season with Real on July 27, albeit working at a different rate to the others."

A week ago Real said Ronaldo would not need surgery on his knee and that they had advised him to rest.

Real's next game is a friendly against Real-Salt Lake in the United States on Aug. 12.

Ronaldo struggled with minor health problems and suggestions he was overweight before the World Cup, where Brazil were knocked out in the quarter-finals by France.

Two goals against Japan and one against Ghana allowed him to break the World Cup scoring record with 15 goals in the finals.