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 number nine 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 in a statement. "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 number one Caroline Wozniacki, Maria Sharapova, Victoria Azarenka, Petra Kvitova, Vera Zvonareva, Samantha Stosur and Li Na in Istanbul next week.