Simona Halep: World number one withdraws from WTA Finals with back injury
World number one Simona Halep has withdrawn from next week's WTA Finals because of a lower back injury.
The Romanian sustained the injury - a herniated disc - during a training session before last month's Wuhan Open.
"I'm not ready to compete at this level and I'm still sore," the 27-year-old said. "I didn't practise for the last four weeks."
World number 10 Kiki Bertens takes Halep's place in the event, where $7m (£5.34m) prize money is available.
Halep added: "It's always difficult to withdraw from a big tournament. Actually, I think it's the first time in my life. So it was a tough decision but it's better for my health."
The French Open champion received treatment on the back problem during her defeat by Dominika Cibulkova in the second round of the Wuhan Open and then withdrew when one set down to Tunisia's Ons Jabeur in the first round of the China Open.
It means Bertens will get to compete in the singles competition at the season-ending WTA Finals in Singapore, which begin on 21 October.
The 26-year-old is the first Dutch woman to break into the world's top 10 since Brenda Schultz-McCarthy in 1996.
"I'm very happy with my season and to finish it off at the WTA Finals is the ultimate prize," said Bertens. "I have great memories in Singapore from reaching the doubles final last year."
Bertens lost in the doubles final alongside Sweden's Johanna Larsson last year.
She will join Angelique Kerber, Naomi Osaka, Petra Kvitova, Caroline Wozniacki, Sloane Stephens, Karolina Pliskova and Elina Svitolina in the singles competition this time around.
The eight players will be split into two round-robin groups, with group winners and runners-up reaching the semi-finals.