World number six Marketa Vondrousova (24) suffered an injury setback less than two weeks before her Wimbledon title defence when she was forced to retire from her Berlin Ladies Open second-round match against Russian Anna Kalinskaya on Thursday.
The Czech was leading 5-3 in the opening set before she slipped and retired at 5-5 with what appeared to be a hip problem.
Kalinskaya, ranked 24th, will face either twice Grand Slam champion Aryna Sabalenka or Daria Kasatkina of Russia in the quarter-finals.
It was, however, a good day for 2022 Wimbledon champion Elena Rybakina as she beat Veronika Kudermetova 6-4 7-5. Other top-ranked players, including Coco Gauff, Jessica Pegula and Ons Jabeur, also advanced.
Wimbledon runs from July 1-14.
