Real Madrid's Dutch striker Ruud van Nistelrooy underwent surgery Wednesday to repair an ankle injury and could be out of action for six weeks, the club announced.

Van Nistelrooy "today underwent an exploratory atroscopic operation on his right ankle due to the chronic synovitis which he is suffering," Real said in a statement on its website.

It said the operation, which took place in Amsterdam, was successful. Real said the striker may be out of action for the next six weeks, but could be fit in time for the club's home match with rivals Barcelona on 7 May.

The Dutchman, league top scorer last season, has not played for almost a month already. This season he has hit a dozen league goals, but has not found the target since January 20. Raul is the club's top marksman this season with 13 in La Liga.

Despite a weekend loss to La Coruna, the meringues, who are defending champions, have a seven-point lead over second-placed Barcelona.