(CNN) -- Serena Williams was forced to pull out of the Madrid Open with a thigh injury ahead of her quarter final tie with Petra Kvitova Friday. 

The withdrawal will come as a blow to the world No. 1's preparations for the French Open with the year's second major beginning in two weeks' time. 

Williams had been playing with heavy strapping all week, although confirmed she hopes to be able to take part in the Italian Open in Rome next week. 

"I have a left thigh injury and, unfortunately, have to withdraw from this year's Madrid Open," Williams told the WTA website. 

"It happened during my first round match. It started to get better, but most importantly right now, I just need some time to rest and recover. 

"I am planning to play in Rome. Fortunately, I have a bye next week so will have an extra day of rest." 

Williams has won the title in Madrid for the last two years and used the event as a springboard to take the French Open crown at Roland Garros last May. 

She added: "It's beyond words. It's so frustrating. We couldn't ask for a better tournament and I love it here in Madrid. I love being a champion here." 

Elsewhere in the women's draw, Maria Sharapova overcame world No. 2 Li Na 2-6, 7-6 (7/5) 6-3 to reach the semifinals where she will face Poland's Agnieszka Radwanska who defeated surprise package Caroline Garcia 6-4, 4-6, 6-4. 

Williams' withdrawal means the second semifinal will pit Kvitova against No.4 seed Simona Halep who trumped the in-form Ana Ivanovic 6-2, 6-2. 
What was she wearing in play earlier in the week?
unknown