Aryna Sabalenka and Ons Jabeur on Saturday became the latest top-10 players to retire from the Berlin Open because of injury or illness, after Wimbledon champions Elena Rybakina and Marketa Vondrousova also withdrew this week.
Sabalenka was forced to retire from her quarterfinal against Russia's Anna Kalinskaya because of shoulder pain when the Belarusian trailed 5-1 in the opening set.
It marked the first time in her WTA Tour career that Sabalenka had retired from a match because of injury.
Kalinskaya has reached the semifinals with two walkovers after Wimbledon champion Vondrousova slipped and fell during their last-16 match, forcing the Czech player to retire.
Jabeur, meanwhile, was involved in a 72-minute opening set in her quarterfinal with Coco Gauff that the American won 7-6 (9) before the Tunisian retired because of illness.
Jabeur was seen getting her temperature checked before she retired.
"It doesn't feel like a win, especially because we had such a great first set. I wish Ons the best," Gauff said after reaching the semifinals. "I think it's something that's just going to happen today and she'll feel better tomorrow. I think she'll be strong at Wimbledon."
On Friday, Rybakina withdrew because of illness, sending Belarusian Victoria Azarenka through to the semifinals. Rybakina was visibly struggling with what appeared to be abdominal pains.
Several quarterfinals were pushed to Saturday because of rain. Following Sabalenka's exit, Kalinskaya moved on to Azarenka and beat the former No. 1 player 6-1, 6-7 (3), 6-1 to earn a spot in Sunday's final.
No. 5 Jessica Pegula was leading doubles partner and No. 2 Gauff 7-5, 6-6 (3-1) when rain suspended their semifinal. The match will resume on Sunday.
Information from Reuters and The Associated Press was used in this report.