Andre Agassi has an injured thigh that forced him to withdraw on Tuesday from a Wimbledon tuneup two days after winning the French Open.
Agassi plans to return to the United States for treatment and intends to play Wimbledon, which starts June 28.
He consulted the tournament doctor at the Gerry Weber Open before dropping out because of a pulled muscle in his right thigh.
"It's a great disappointment for me," Agassi said. "I thought two days of rest would be enough."
"I'd already felt it after the third round in Paris," he added. "This morning I thought it was only a sore muscle but unfortunately it is not. I don't want to take any risks."
Agassi won Wimbledon in 1992, his first Grand Slam title. He added the U.S. Open in 1994, the Australian Open in 1995 and this past French Open, giving him a career Grand Slam.
Agassi was the major attraction of the Halle tournament, with tickets sales rising sharply after his French Open victory.
The tournament tries to recreate Wimbledon conditions. But the center court has a retractable roof and it was much in use Tuesday as intermittent rain hit the grass-court event.
Richard Krajicek, the 1996 Wimbledon champion from the Netherlands who is seeded third, was among three seeded players upset in the first round of the $900,000 tournament.
Daniel Vacek of the Czech Republic beat Krajicek 7-6 (8-6), 6-4; Sjeng Schalken of the Netherlands ousted No. 8 Jerome Golmard of France 7-5, 6-0; and Gianluca Pozzi of Italy routed Felix Mantilla, the fifth-seeded clay-court specialist from Spain, 6-2, 6-2.
One seeded player to advance was No. 6 Tommy Haas. The German saved three set points in the second set to defeat France's Guillaume Raoux 6-4, 7-5.
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