Serena Williams of the U.S. celebrates her victory over Victoria Azarenka of Belarus at the end of their women's final match at the Madrid Open tennis tournament May 13, 2012. (Photo: Reuters)
Serena Williams said she expected to be 100 percent fit for next week's French Open despite withdrawing from the Italian Open on Saturday because of a back injury.
The American had been due to play China's Li Na in the first semi-final but told a news conference she was pulling out as a precaution.
"On Friday morning I felt a bit of pain in my lower back and if it's not 100 percent it's better not to play and make it worse," the world number six said.
"But I am in good form, I have a few days to get better and I am confident I will be 100 percent fit for the French Open."
Williams played only four games in the previous round as Flavia Pennetta of Italy retired with a wrist problem.
"Yesterday I might have had to retire as well," Williams said. "I don't know because we only played a bit and I didn't have time to check my condition."
Williams, who has won claycourt titles in Charleston and Madrid in the past month, said she needed to be careful not to over-play, having been out of the game for a year in 2010 and 2011 because of a blood clot on one of her lungs.
French Open holder Li will go through to play either Maria Sharapova of Russia or Germany's Angelique Kerber in the final.
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