World number one Amelie Mauresmo withdrew from the Zurich Open on Thursday with a right shoulder injury and said she might not be fit to defend her title at the WTA Championships next month.

"It's very frustrating," the Frenchwoman told reporters. "Two weeks ago I could already feel something and I could feel it on the serve, and yesterday I was not serving very hard and I could feel something again in the second set.

"I've pushed myself to play last week and to be able to come here this week. Maybe it was not the right solution. There is inflammation in two areas of the shoulder but not big damage that could really put me out for a long time."

"I hope I will be in Madrid," Mauresmo added. "For me of course it's an important goal. I definitely hope I will be ready. I can't say for sure today that I'm going to be but I'll do my best and hopefully it will work."

On Wednesday, Mauresmo had struggled to overcome Australia's Samantha Stosur to reach the Zurich quarter-finals, hitting five double-faults.

Mauresmo, who made the biggest breakthrough of her career by winning the WTA Championships last year, withdrew from the Stuttgart tournament earlier this month but played in Moscow [Images] last week before falling to Czech Nicole Vaidisova in the quarter-finals.

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