'The initial indications are that the procedure was successful,' United said in a statement.

'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.'

Hospital spokesman Johan Kortenray said that Ronaldo is expected to leave the Academic Medical Centre today.

Ronaldo, 23, could miss the start of the Premier League season next month.

The Portuguese revealed after last month's European Championship that he had been playing in pain for the last three months.

He scored 42 goals for the Red Devils last season as he powered them to triumphs in the Premier League and Champions League.

But, at Euro 2008, Portugal were ousted in the quarter-finals.

The ankle surgery comes as speculation continues about a possible move to Real Madrid for Ronaldo.

Real president Ramon Calderon said on Sunday he was ready to begin transfer talks with United, but was not confident about signing the winger even if United consented.

While Ronaldo has stoked up the possibility of moving to the Spanish champions, no transfer request has been submitted and United have vowed to retain the player.

'In theory, there is time as there are two months to the end of August, if Manchester United get in contact with us and offer him,' said Calderon at Wimbledon, where he was watching the men's tennis singles final between Rafael Nadal and Roger Federer.

'Even if they do say he is for sale, we don't know if we can complete the deal.'

ASSOCIATED PRESS, REUTERS