Organisers say Juan Martin del Potro of Argentina has withdrawn from Queen’s in London because of a knee injury.

The tennis tournament, a key warm-up event for Wimbledon, starts on Monday.

The No.9-ranked del Potro appeared to have been hampered by a left knee injury during his French Open quarter-final defeat to Roger Federer on Tuesday.

The Argentine’s left knee was heavily wrapped in white tape during the match but he refused to blame the injury for his Roland Garros exit.