Denmark's Caroline Wozniacki holds a press conference after withdrawing from the WTA Championships semi-final tennis match against Serena Williams of the US at the Khalifa International Tennis and Squash Complex in Doha on October 31, 2009. Wozniacki was forced to retire with a stomach injury at the start of the second set. AFP PHOTO/KARIM JAAFAR (Photo credit should read KARIM JAAFAR/AFP/Getty Images)

Denmark's Caroline Wozniacki laughs as she holds a press conference after withdrawing from the WTA Championships semi-final tennis match against Serena Williams of the US at the Khalifa International Tennis and Squash Complex in Doha on October 31, 2009. Wozniacki was forced to retire with a stomach injury at the start of the second set. AFP PHOTO/KARIM JAAFAR (Photo credit should read KARIM JAAFAR/AFP/Getty Images)

Denmark's Caroline Wozniacki eyes the ball before returning it to Serena Williams of the US during their WTA Championships semi-final tennis match at the Khalifa International Tennis and Squash Complex in Doha on October 31, 2009. Wozniacki was forced to retire with a stomach injury at the start of the second set. AFP PHOTO/KARIM JAAFAR (Photo credit should read KARIM JAAFAR/AFP/Getty Images)

Denmark's Caroline Wozniacki returns the ball to Serena Williams of the US during the WTA Championships semi-final tennis match at the Khalifa International Tennis and Squash Complex in Doha on October 31, 2009. Wozniacki was forced to retire with a stomach injury at the start of the second set. AFP PHOTO/KARIM JAAFAR (Photo credit should read KARIM JAAFAR/AFP/Getty Images)

Denmark's Caroline Wozniacki eyes the ball before returning it to Serena Williams of the US during their WTA Championships semi-final tennis match at the Khalifa International Tennis and Squash Complex in Doha on October 31, 2009. Wozniacki was forced to retire with a stomach injury at the start of the second set. AFP PHOTO/KARIM JAAFAR (Photo credit should read KARIM JAAFAR/AFP/Getty Images)

Denmark's Caroline Wozniacki eyes the ball before returning it to Serena Williams of the US during their WTA Championships semi-final tennis match at the Khalifa International Tennis and Squash Complex in Doha on October 31, 2009. Wozniacki was forced to retire with a stomach injury at the start of the second set. AFP PHOTO/KARIM JAAFAR (Photo credit should read KARIM JAAFAR/AFP/Getty Images)

Denmark's Caroline Wozniacki squats during the WTA Championships semi-final tennis match against Serena Williams of the US at the Khalifa International Tennis and Squash Complex in Doha on October 31, 2009. Wozniacki was forced to retire with a stomach injury at the start of the second set. AFP PHOTO/KARIM JAAFAR (Photo credit should read KARIM JAAFAR/AFP/Getty Images)

Denmark's Caroline Wozniacki withdraws from the WTA Championships semi-final tennis match against Serena Williams of the US following a stomach injury at the Khalifa International Tennis and Squash Complex in Doha on October 31, 2009. AFP PHOTO/KARIM JAAFAR (Photo credit should read KARIM JAAFAR/AFP/Getty Images)

Denmark's Caroline Wozniacki receives medical aid during the WTA Championships semi-final tennis match against Serena Williams of the US at the Khalifa International Tennis and Squash Complex in Doha on October 31, 2009. Wozniacki was forced to retire with a stomach injury at the start of the second set. AFP PHOTO/KARIM JAAFAR (Photo credit should read KARIM JAAFAR/AFP/Getty Images)

A general shot of the Khalifa International Tennis and Squash Complex during the WTA Championships tennis match between Denmark's Caroline Wozniacki and Jelena Jankovic of Serbia in Doha on October 30, 2009. Jankovic won the match 6-2, 6-2.AFP PHOTO/KARIM JAAFAR (Photo credit should read KARIM JAAFAR/AFP/Getty Images)

Denmark's Caroline Wozniacki returns to Jelena Jankovic of Serbia during their WTA Championships tennis match at the Khalifa International Tennis and Squash Complex in Doha on October 30, 2009. Jankovic won the match 6-2, 6-2.AFP PHOTO/KARIM JAAFAR (Photo credit should read KARIM JAAFAR/AFP/Getty Images)

Denmark's Caroline Wozniacki returns to Jelena Jankovic of Serbia during their WTA Championships tennis match at the Khalifa International Tennis and Squash Complex in Doha on October 30, 2009. Jankovic won the match 6-2, 6-2.AFP PHOTO/KARIM JAAFAR (Photo credit should read KARIM JAAFAR/AFP/Getty Images)

Denmark's Caroline Wozniacki returns to Jelena Jankovic of Serbia during their WTA Championships tennis match at the Khalifa International Tennis and Squash Complex in Doha on October 30, 2009. Jankovic won the match 6-2, 6-2.AFP PHOTO/KARIM JAAFAR (Photo credit should read KARIM JAAFAR/AFP/Getty Images)

Denmark's Caroline Wozniacki serves to Jelena Jankovic of Serbia during their WTA Championships tennis match at the Khalifa International Tennis and Squash Complex in Doha on October 30, 2009. Jankovic won the match 6-2, 6-2.AFP PHOTO/KARIM JAAFAR (Photo credit should read KARIM JAAFAR/AFP/Getty Images)

Denmark's Caroline Wozniacki gestures during her tennis match against Jelena Jankovic of Serbia at the WTA Championships at the Khalifa International Tennis and Squash Complex in Doha on October 30, 2009. Jankovic won the match 6-2, 6-2.AFP PHOTO/KARIM JAAFAR (Photo credit should read KARIM JAAFAR/AFP/Getty Images)

Denmark's Caroline Wozniacki attends the tennis match against Jelena Jankovic of Serbia during the WTA Championships at the Khalifa International Tennis and Squash Complex in Doha on October 30, 2009. Jankovic won the match 6-2, 6-2.AFP PHOTO/KARIM JAAFAR (Photo credit should read KARIM JAAFAR/AFP/Getty Images)

Denmark's Caroline Wozniacki returns to Jelena Jankovic of Serbia during their WTA Championships tennis match at the Khalifa International Tennis and Squash Complex in Doha on October 30, 2009. Jankovic won the match 6-2, 6-2.AFP PHOTO/KARIM JAAFAR (Photo credit should read KARIM JAAFAR/AFP/Getty Images)

Denmark's Caroline Wozniacki serves to Jelena Jankovic of Serbia during their WTA Championships tennis match at the Khalifa International Tennis and Squash Complex in Doha on October 30, 2009. Jankovic won the match 6-2, 6-2.AFP PHOTO/KARIM JAAFAR (Photo credit should read KARIM JAAFAR/AFP/Getty Images)

Denmark's Caroline Wozniacki serves to Jelena Jankovic of Serbia during their WTA Championships tennis match at the Khalifa International Tennis and Squash Complex in Doha on October 30, 2009. Jankovic won the match 6-2, 6-2.AFP PHOTO/KARIM JAAFAR (Photo credit should read KARIM JAAFAR/AFP/Getty Images)

Denmark's Caroline Wozniacki serves to Jelena Jankovic of Serbia during their WTA Championships tennis match at the Khalifa International Tennis and Squash Complex in Doha on October 30, 2009. Jankovic won the match 6-2, 6-2.AFP PHOTO/KARIM JAAFAR (Photo credit should read KARIM JAAFAR/AFP/Getty Images)

Denmark's Caroline Wozniacki lies on the ground from a cramp in her leg during her WTA Championships tennis match against Vera Zvonareva of Russia in Doha on October 29, 2009. The Danish teenager overcame crippling cramp to reach the WTA Championships semi-finals defeating Russia's late call-up Vera Zvonareva 6-0, 6-7 (3/7), 6-4. TOPSHOTS/AFP PHOTO/KARIM JAAFAR (Photo credit should read KARIM JAAFAR/AFP/Getty Images)

Denmark's Caroline Wozniacki lies on the ground from a cramp in her leg during her WTA Championships tennis match against Vera Zvonareva of Russia in Doha on October 29, 2009. The Danish teenager overcame crippling cramp to reach the WTA Championships semi-finals defeating Russia's late call-up Vera Zvonareva 6-0, 6-7 (3/7), 6-4. AFP PHOTO/KARIM JAAFAR (Photo credit should read KARIM JAAFAR/AFP/Getty Images)

Denmark's Caroline Wozniacki tries to get up from the ground after a cramp in her leg during her WTA Championships tennis match against Vera Zvonareva of Russia in Doha on October 29, 2009. The Danish teenager overcame crippling cramp to reach the WTA Championships semi-finals defeating Russia's late call-up Vera Zvonareva 6-0, 6-7 (3/7), 6-4. AFP PHOTO/KARIM JAAFAR (Photo credit should read KARIM JAAFAR/AFP/Getty Images)

Denmark's Caroline Wozniacki reacts to a cramp in her leg during her WTA Championships tennis match against Vera Zvonareva of Russia in Doha on October 29, 2009. The Danish teenager overcame crippling cramp to reach the WTA Championships semi-finals defeating Russia's late call-up Vera Zvonareva 6-0, 6-7 (3/7), 6-4. AFP PHOTO/KARIM JAAFAR (Photo credit should read KARIM JAAFAR/AFP/Getty Images)

Denmark's Caroline Wozniacki reacts to a cramp in her leg during her WTA Championships tennis match against Vera Zvonareva of Russia in Doha on October 29, 2009. The Danish teenager overcame crippling cramp to reach the WTA Championships semi-finals defeating Russia's late call-up Vera Zvonareva 6-0, 6-7 (3/7), 6-4. AFP PHOTO/KARIM JAAFAR (Photo credit should read KARIM JAAFAR/AFP/Getty Images)

Denmark's Caroline Wozniacki reacts after winning against Vera Zvonareva of Russia during their WTA Championships tennis match in Doha on October 29, 2009. The Danish teenager overcame crippling cramp to reach the WTA Championships semi-finals defeating Russia's late call-up Vera Zvonareva 6-0, 6-7 (3/7), 6-4. AFP PHOTO/KARIM JAAFAR (Photo credit should read KARIM JAAFAR/AFP/Getty Images)

Denmark's Caroline Wozniacki reacts after winning against Vera Zvonareva of Russia during their WTA Championships tennis match in Doha on October 29, 2009. The Danish teenager overcame crippling cramp to reach the WTA Championships semi-finals defeating Russia's late call-up Vera Zvonareva 6-0, 6-7 (3/7), 6-4. AFP PHOTO/KARIM JAAFAR (Photo credit should read KARIM JAAFAR/AFP/Getty Images)

Denmark's Caroline Wozniacki reacts after winning against Vera Zvonareva of Russia during their WTA Championships tennis match in Doha on October 29, 2009. The Danish teenager overcame crippling cramp to reach the WTA Championships semi-finals defeating Russia's late call-up Vera Zvonareva 6-0, 6-7 (3/7), 6-4. AFP PHOTO/KARIM JAAFAR (Photo credit should read KARIM JAAFAR/AFP/Getty Images)

Denmark's Caroline Wozniacki reacts after winning against Vera Zvonareva of Russia during their WTA Championships tennis match in Doha on October 29, 2009. AFP PHOTO/KARIM JAAFAR (Photo credit should read KARIM JAAFAR/AFP/Getty Images)

Caroline Wozniacki of Denmark is pictured during her WTA Championships tennis match against Vera Zvonareva of Russia in Doha on October 29, 2009. AFP PHOTO/KARIM JAAFAR (Photo credit should read KARIM JAAFAR/AFP/Getty Images)