Wimbledon champion Simona Halep retired from the Wuhan Open after sustaining a lower back injury in her third-round match against Elena Rybakina in China.
The world number six, who ended the year as world number one in 2017 and 2018, withdrew when trailing 5-4 in the first set against the Kazakh wildcard.
Meanwhile, Australian top seed Ashleigh Barty qualified for the quarter finals with a 6-3 7-5 win against Sofia Kenin.
Third seed Elina Svitolina also progressed against Svetlana Kuznetsova.
Ukrainian US Open and Wimbledon semi-finalist Svitolina, ranked ninth, won 6-4 6-2 as she continues her battle for a world top-eight spot that would allow her to defend her title at the WTA Finals in Shenzhen in October.
Romanian Halep, currently third in the race to Shenzhen, said that the “sharp pain” in her lower back felt in “the same zone” as the injury which kept her out for three months at the end of 2018.
World number two Karolina Pliskova will compete for a quarter-final spot against Dayana Yastremska later on Wednesday.