Istanbul - World No 2 and top seed Caroline Wozniacki was forced to retire from her Istanbul Cup quarter-final against Pauline Parmentier of France on Friday after suffering an abdominal injury.
Australian Open champion Wozniacki had already received an on-court medical timeout before Parmentier levelled the match at a set apiece.
The Dane opted not to continue with the match finely poised at 4-6, 6-3.
"I saw she had some problems in the second set with the serve. She was not serving full speed. It's tough when you see your opponent not doing well," Parmentier told wtatennis.com.
"Even though we are opponents on the court, we want everyone to be fine, so it's not easy."
Unseeded Parmentier will now face seventh seed Irina-Camelia Begu of Romania who saw off Donna Vekic of Croatia 3-6, 7-6 (7/1), 6-1.
In Saturday's other semi-final, Polona Hercog of Slovenia faces Greece's Maria Sakkari.