World number one Caroline Wozniacki reached the Qatar Open semi-finals, but Simona Halep withdrew because of injury after winning her quarter-final.
Dane Wozniacki, the Australian Open champion, beat Germany's Angelique Kerber 7-6 (7-4) 1-6 6-3.
World number two Halep beat American CiCi Bellis 6-0 6-4, but then revealed she had a right foot injury.
"It's going to be dangerous if I force it," said the Romanian, who is out until at least Indian Wells in March.
"I am surprised that I could play three matches and to win them. I felt pain every day."
Halep said it is the same injury that affected her run to the Australian Open final in January.
"The MRI shows that I have fluid and also tendinitis at the fourth toe, so I have just to take care of it and think about my health first," added the 26-year-old.
Halep's withdrawal means fourth seed Garbine Muguruza, who beat Caroline Garcia 3-6 6-1 6-4, will go straight through to Sunday's final.
Czech Petra Kvitova reached the semi-finals after Germany's Julia Gorges retired from their quarter-final while trailing 6-4 2-1.
By reaching the semi-finals, Wozniacki became just the fourth woman in history to pass $30m (£21m) in prize money.