BEIJING, China - World No.1 Simona Halep's week at the China Open ended after just one set on Sunday, as she was forced to retire due to a continuing back injury against Tunisia's Ons Jabeur.

"There is a pain. I couldn't move properly, so that's why I stopped. I don't know exactly what it is. I will go home. I will have an MRI and I will see," the World No.1 said after the match.

"I'm just worried now. I feel sad that I couldn't finish. That's why I stopped, because I felt like it's getting worse if I continue. It's really tough when you have back injury because you cannot bend, you cannot react at the balls. I couldn't play."

Halep also struggled with the injury last week at the Dongfeng Motor Wuhan Open, where she lost her opening match against Dominika Cibulkova, but did complete the match.

"Today I could stop. I think last week was also good point to stop, but I forced a little bit to see how it goes. But here it was a bit too much," she added. 

"In Wuhan, the lower back was blocked so I couldn't move for two days there. Then with a lot of treatment, it was better. I started to feel in the muscle a lot, and it was really, really contracted. I did the treatment, and the muscle was better, but now I still feel the bone."

The retirement win is Jabeur's second career victory against a Top 10 player, having also defeated then-World No.7 Dominka Cibulkova at the French Open last year.

"I didn't want the match to end like this. I wanted a real battle. Unfortunately, she was injured. I didn't look happy because I didn't want to win this way," Jabeur said. "I hope next time we can play a real match without anyone injured."

It was the second match to end by retirement on Sunday in Beijing, as Daria Kasatkina retired with gastrointestinal illness against Germany's Laura Siegemund when trailing, 6-3, 4-2.