(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.

Now, provide a numbered list of answers to these questions:

1. Did Serena Williams withdraw from the Madrid Open?
2. Why?
3. What part of her was injured?
4. Who was she going to play on Friday?
5. What was she wearing in play earlier in the week?
6. What is she hoping to take part in next week?
7. Where?
8. Who did Maria Sharapova overcome?
9. Who did Radwanska defeat?
10. Where is Radwanska from?
11. When did Williams' injury happen?
12. Then what happened to it?
13. What does she need now?
14. ANything else?
15. Where is the French Open held?
16. When?
17. How many times has Williams won Madrid?
18. Does she hate it there?
19. Which website was Williams talking to?
20. For Williams, Madrid was a springboard for what?
1. yes
2. an injury
3. a thigh
4. Petra Kvitova
5. unknown
6. Italian Open
7. Rome
8. Li Na
9. Caroline Garcia
10. Poland
11. her first round match
12. It started to get better
13. some time
14. rest
15. Roland Garros
16. May
17. two
18. no
19. the WTA's
20. to take the French Open crown