World number one Simona Halep has withdrawn from next week’s WTA Finals because of a lower back injury.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) of 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.”

More to follow.