Marat Safin beat wildcard Alexander Popp in the first round of the Gerry Weber Open before admitting he may have to cut short his grass-court season. The Russian, seeded second, cruised past the German 6-3 6-2, and faces Andrei Pavel or Fabrice Santoro next.
But he admitted in Halle that he has a mystery knee injury and would "not continue playing through pain".
"Writing off the grass-court season is an option, and maybe I'll just skip Wimbledon and use the time to recover."
Safin added: "I have been bothered by this knee injury for almost two months and no doctor can tell me exactly what the nature is.
"It's no fun when you're out there playing through pain, using pain-killers all the time."
In other games in Halle, fourth seed Guillermo Canas beat Fernando Verdasco 6-4 6-4.
Roger Federer and Rafael Nadal start their campaigns later in the week and could go on to face each other in the semis as they did at the French Open.
"I hope (Nadal) stays in the tournament for a long time and a rematch is possible," said Federer, who has won at Halle the last two years and has, himself, not lost on grass for 24 successive matches.
"Of course I would be the favourite because this surface is very special for me," Federer added.
Nadal has beaten the Swiss twice in their three meetings, with Federer coming from two sets down to win their other encounter. They have never met on grass.
"Clearly my goal is a hat-trick of wins at (Halle)," Federer said. "I want to win the title and help build up my confidence for Wimbledon."
MMIX
E-mail this to a friend 
Printable version 