Victoria Azarenka, who lost in the Carlsbad Open final to Sam Stosur on Sunday, has pulled out of the Rogers Cup in Toronto with a lower back injury, the tournament announced.

The world number two had been playing in her first tournament since Wimbledon, where she was forced to pull out of her second round match due to knee and hip injuries.

"I'm so disappointed that I can't make it to Toronto as I added it to my schedule knowing what an important event it is," said Azarenka.

The tournament begins on Monday.

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