Maria Sharapova withdrew from the Italian Open before her quarter-final with Italy's Sara Errani on Friday because of "physical problems", organisers said.
The Russian is set to defend her French Open title later this month.
Italian Open officials did not elaborate further on the reasons for Sharapova's Rome exit but the 26-year-old said on her Twitter account she was sick.
"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 tweeted.
"It really is one of my favourite tournaments during the year and I can't wait to be back next year."