Manchester United winger Cristiano Ronaldo has had 'successful' surgery on his ankle in Amsterdam, the club confirmed in a statement on Monday.

'Initial indications are that the procedure was successful,' United said after the Portuguese star went under the knife in an op which could see the 23-year-old miss the start of the new season.

'Cristiano will begin his convalescence under the direction of club medical staff and an estimation of his return to full fitness will be possible following review by the specialist in one month,' United said in their statement.

Earlier, Johan Kortenray, press spokesman at the Amsterdam hospital where the striker is being treated, indicated that Ronaldo would likely be allowed to go home on Tuesday.

The operation, carried out by renowned Dutch orthopaedic surgeon Niek van Dijk, was arranged after the view of a specialist backed up that of medical staff from both Manchester United and the Portuguese Football Association that it was required.

Portuguese sports newspaper A Bola earlier indicated that two fragments of cartilage have floated free, causing recurrent inflammation.

Ronaldo, a target for Real Madrid - though the Spanish club say they expect him to stay at Old Trafford at least for next season - revealed following Portugal's Euro 2008 exit that he had been suffering from the injury for some time.