Knee problems hamper Nadal

World number two Rafael Nadal could join the list of high-profile withdrawals from the Madrid Masters Tennis Series if the tendinitis in his knees does not improve before his opening match today.

The 19-year-old top seed withdrew from the ATP event in Vienna last week. Although he said he was determined to play in the Madrid tournament the pain in his knees could cause him to drop out again.

The two million euro hardcourt tournament has been hit by the withdrawal of some of the biggest attractions on the circuit. Roger Federer, Lleyton Hewitt, Andre Agassi and last year's winner Marat Safin have all pulled out because of injury.