Poland's Agnieszka Radwanska secured the last remaining spot in the season-ending WTA Championships without hitting a ball after Marion Bartoli 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 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 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, Maria Sharapova, Victoria Azarenka, Petra Kvitova, Vera Zvonareva, Samantha Stosur and Li Na in Istanbul next week.