Madrid - Fourth seed Victoria Azarenka withdrew with lower back pain from the Madrid Open on Wednesday, handing a place in the quarter-finals to qualifier Louisa Chirico.
Azarenka from Belarus, winner of back-to-back March titles at Indian Wells and Miami, had advanced at the Caja Magica with a pair of straight-set wins, losing just 11 games.
The WTA number five lost Madrid finals in 2011 and 2012.
Her pullout came on the day that holder and two-time champion Petra Kvitova lost in the third round, going out to Australian Daria Gavrilova 6-3, 6-4.
Azarenka joins Roger Federer in pulling out of one of the final major tune-ups prior to the May 22 start of the French Open due to back problems.
"I tweaked my back in my first match, it was cold that day," said Azarenka.
"In my second match, I was in a lot of discomfort. I thought a day off would help, but today during a hit it came back again.
"I just don't feel I'm able to compete today."
Azarenka was unsure if she would be able to play Rome, which begins on Monday.
"I want to make a smart decision for the big picture.
"I have to take it day by day and see if my body's ready. I'll hope to take tests today so we can take action."