Del Potro out of Queen's event

London - Organisers say Juan Martin del Potro of Argentina has withdrawn from the Aegon championships at Queen's Club in London because of knee injury.

The tournament, which is a warm-up event for Wimbledon, starts on Monday.

The No 9-ranked Del Potro appeared to have been hampered by a left knee during a French Open quarter-final match against Roger Federer Tuesday.

The Argentine's left knee was heavily wrapped in white tape during the match he had lost, although Del Potro refused to place any blame on the injury for the defeat at Roland Garros.