Kim Clijsters withdrew from the Unicef Open before the semifinals on Friday because of a stomach muscle strain, saying she did not want to jeopardize playing in her last Wimbledon before retirement.

Clijsters' physiotherapist, Sam Versleghers, said the 29-year-old Belgian felt the injury on Thursday during her tough two-set quarterfinal against Francesca Schiavone.

The announcement came just hours before Clijsters was due to play Urszula Radwanska, who subsequently advanced to the final.

"This is a decision taken with my head, not my heart," Clijsters said in a statement. "But preventatively withdrawing from this tournament is the right decision. I am definitely going to play at Wimbledon."

The four-time Grand Slam winner is unseeded at Wimbledon for the first time since 2000 and has a tough first-round draw against 18th-seeded Jelena Jankovic of Serbia.

Clijsters said earlier this year she intends to retire after the US Open, which she won in 2005, 2009 and 2010. She also won the Australian Open in 2011.

On court Friday, Philipp Petzschner of Germany beat Xavier Malisse of Belgium 7-5, 7-5 to become the first finalist.

He will meet top-seeded David Ferrer in Saturday's final after the Spaniard beat Benoit Paire of France 7-6, 3-6, 6-1.

Kirsten Flipkens kept Belgian hopes alive by beating Roberta Vinci of Italy 6-4, 7-6 (5) in a quarterfinal halted by rain on Thursday night, but she later lost 6-4, 6-2 to Nadia Petrova of Russia.