Spain's 75-year-old King Juan Carlos recovered in hospital Wednesday after hip-replacement surgery but now faces yet another operation, feeding concerns over his future as head of state.

Doctors said he was in "highly satisfactory" condition after a surgeon fitted a temporary replacement for an implant that had got infected -- his eighth operation in just over three years.

But news that a further operation would be needed after two months to insert a permanent implant kept alive speculation of a possible abdication, despite the palace's denials.

Prime Minister Mariano Rajoy said the government had no plans to try to regulate the role of the king's son and heir Felipe, 45, in case Juan Carlos is incapable of ruling.

"Absolutely not, we have no intention of doing that," Rajoy told reporters late Tuesday in New York where he was attending a United Nations general assembly. "There is no reason to do so."

US-based hip specialist Miguel Cabanela gave the monarch a new artificial left hip coated in antibiotics to fight the infection, said a statement from the palace on Wednesday.

The king has appeared on crutches looking frail while keeping up his schedule of public appearances over recent weeks, after the previous implant fitted last November became painful.

But he has kept up a jovial front.

"He is very lively and keen to get back on his feet as soon as the doctors let him," Felipe said after visiting his father in hospital on Wednesday with his wife, Princess Letizia.

The palace said in a statement: "His majesty had a good night. He left intensive care and has been in the ward since this morning," after the operation at Quiron Hospital in the western Madrid suburbs.

"His progress is highly satisfactory, his blood circulation is stable, he is comfortable and in good spirits."

Cabanela told reporters the king would be in hospital for up to eight days and would need a new operation to receive a permanent prosthetic hip after eight weeks. He could then be walking again a further six weeks later.

Scandals and speculation

The king's ailing health, on top of recent royal scandals, has sparked debate about what to do if the king is incapacitated and whether he should hand over power to Felipe.

Announcing news of the operation last week, the palace said Juan Carlos had at no time considered abdicating nor handing over power.

Juan Carlos is widely respected for his role in guiding Spain's transition to democracy after the death of dictator General Francisco Franco in 1975.

But his image has suffered in particular because of a corruption scandal implicating his youngest daughter Cristina and her husband Inaki Urdangarin.

Under investigation since late 2011 for alleged embezzlement of public funds, Urdangarin has appeared in court for questioning but has not been formally charged with any crime. The judge probing the case has ordered a report on Cristina's tax affairs.

The king himself sparked outrage last year for taking an expensive elephant-hunting holiday in Botswana, while Spain struggled through a recession with one in four people out of work.

He broke his right hip during the trip and had to be flown home for surgery, after which he made an unprecedented public apology.

The hunting trip threw the spotlight on the royal family's deluxe lifestyle and the king's friendship with Corinna zu Sayn-Wittgenstein, a German aristocrat 28 years his junior, who reportedly accompanied him to Botswana.

Juan Carlos will now almost certainly miss appearing at Spain's national day celebrations on October 12 and the annual Iberoamerican summit of Spanish, Portuguese and Latin American leaders in Panama from October 18-19.

Antonio Torres del Moral, a law expert at Spain's UNED University, told AFP Spain's constitution did not state clearly how the prince might be allowed to take over state functions as regent.

The question has been openly debated in the media and television debates over recent days following news of the king's latest operation.

The expert said abdication, on the other hand, "is a relatively simple mechanism, which must be used if the circumstances require it, as I fear they are gradually starting to."