Reigning French Open champion Justine Henin-Hardenne has withdrawn from the next two tournaments on the women's tour with a hamstring injury.
Henin-Hardenne's season has been marred by injury
The Belgian may now be doubtful for the season-ending Tour Championships.
Henin-Hardenne has been dogged by illness and injury over the past two years but returned to win her second French Open title in June.
She said: "I can't say what will happen with the Masters. I know I am not in the best condition to defend my title."
Henin-Hardenne will miss the Zurich Open and the Generali Ladies Linz championship.
"I realise I'm just not in good enough condition to do well," she said.
"First off, the hamstring injury is still sore and secondly I'm well behind in my preparation."
She added: "For the (Los Angeles) Masters (on 7 November) I can't confirm at this moment. We'll just have to play it by ear."