Roger Federer pulled out of his regular Wimbledon warm-up event in Halle on Monday, blaming fatigue after losing to Rafael Nadal in Sunday's French Open final.

"In an attempt to prevent injury after the long final in Paris, I cannot defend my title at the Gerry Weber Open in Halle," the Swiss world number one wrote on his Web site, www.rogerfederer.com.

"I look forward to returning in 2008."

Federer has won the German grass-court event for the past four years before going on to claim the Wimbledon crown on each occasion.

Organisers said the change in his pre-Wimbledon preparation was down to a problem with his adductor muscles, but an ATP spokesman put the withdrawal down to "general fatigue".

"Of course we really regret it," co-organiser Ralf Weber said at a news conference on Monday. "Roger had played here for the last seven years and he gave everything for the tournament.

"I know Roger took the decision with a heavy heart. He will fly to Zurich, rest a few days and will probably fly straight to London."

Federer had been due to play Olivier Rochus in the first round of the grass-court tournament