World number one Simona Halep has withdrawn from next week's WTA Finals in Singapore because of an ongoing back injury.
The Romanian, who has a herniated disc, had hoped to be fit but is still experiencing pain and will be replaced in the field by Dutchwoman Kiki Bertens.
Halep said: "Unfortunately, after much discussion with my team and doctors, I have made the decision to withdraw from the WTA Finals in Singapore.
"I wanted to finish 2018 on a high after such an incredible year, but sadly my back injury hasn't healed the way we hoped it would and I need to put my long-term health first.
"I'm sad I won't be able to play the fifth and final edition here in Singapore, but I'm confident this is the right decision and will do everything I can to be back fighting for my place at the WTA Finals next year."
Halep has already guaranteed she will finish the year on top of the rankings after a season that brought her a maiden grand slam title at the French Open.
Bertens has had a breakthrough season at the very top level and recently became the first Dutch player to make the top 10 for more than 20 years.
The 26-year-old, who reached the doubles final in Singapore 12 months ago with Swede Johanna Larsson, said: "I'm very happy with my season and to finish it off at the WTA Finals is the ultimate prize. I have great memories in Singapore."
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