Russia's Maria Sharapova has pulled out of the Rome Open, citing "physical problems", the WTA said on Friday.
The two-time winner of the tournament and world number two had been due to play Italy's Sara Errani in the quarter-finals.
Sharapova, the defending champion, posted a message on her Twitter account explaining the reason for her withdrawal.
"I'm sorry for having to withdraw from the tournament this morning. Didn't recover after being sick last week and it got me again last night," Sharapova said.
"It really is one of my favourite tournaments during the year and I can't wait to be back next year!"
Errani, the world number six, will now go through to the semi-finals to meet the winner of the match between Australia's Samantha Stosur and Viktoria Azarenka of Belarus.