Poland's Agnieszka Radwanska [ Images ] secured the last remaining spot in the season-ending WTA Championships without hitting a ball after Marion Bartoli [ Images ] retired from her Kremlin Cup quarter-final with an illness on Friday.

Kremlin Cup organisers said the Frenchwoman was forced to withdraw from her match against Russia's [ Images ] Elena Vesnina after suffering from a viral infection.

World No. 9 Bartoli was the only player with a chance of catching the eighth-ranked Pole but she needed to win in Moscow [ Images ] to clinch a place in the eight-player field in Istanbul.

"I think my whole body needed a break," Bartoli said. "Yesterday, during my match I already didn't feel very well but I still had energy left so it was enough to win."

The third seed had crushed unseeded Russia Ksenia Pervak 6-1, 6-1 in just over an hour on Thursday to reach the last eight.

"This morning I had so much pain in my whole body, in my neck... I couldn't even warm up today. So I knew it would be very difficult (to play today).

"It has been a very long season and I really tried to play till the very end but that was it for me."

Radwanska will join World No. 1 Caroline Wozniacki [ Images ], Maria Sharapova [ Images ], Victoria Azarenka [ Images ], Petra Kvitova [ Images ], Vera Zvonareva [ Images ], Samantha Stosur [ Images ] and Li Na [ Images ] in Istanbul next week.