French Open champion Halep was injured while training at last week's Wuhan Open, where she lost in the second round to Slovakia's Dominika Cibulkova.
Romanian Halep aggravated the problem during her China Open first-round match on Sunday against Ons Jabeur and was forced to retire after losing the first set.
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"I had an MRI on my back and found out I have a disc hernia," Halep said on Twitter.
"I will discuss with doctors in the next few days but hope to be back soon and will keep you updated."
Halep, who won her maiden Grand Slam trophy in Paris this year, became the first player to qualify for the season-ending WTA Finals in Singapore from October 21-28.
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