Serena Williams says she does not expect to be able to return this season reinjuring her foot and pulling out of next week's event in Linz.
"After practicing yesterday morning I felt discomfort in my foot and tests by my doctor revealed that I had unfortunately re-strained it, as a result of over training," said Williams in a statement on her website.
"I am likely out for the year now. I was really looking forward to beginning my comeback in Linz, followed by the Year-end championships in Doha. I feel completely heartbroken, and devastated, but knowing I will never be given more than I can handle I plan on coming back stronger and better."