TORONTO, Aug. 13 (Xinhua) -- World number four Venus Williams has withdrawn from next week's two million-dollar WTA event in Montreal due to a nagging left knee injury, said the American on Friday.

The US veteran also quit this week's Cincinnati Open.

"The pain that I am experiencing in my knee has unfortunately not gone away," the seven-time Grand Slam champion said in a statement.

Venus would have played in Montreal for the first time.

She has not played a top-level singles match since she was eliminated from the Wimbledon quarterfinals by 82nd-ranked Tsvetana Pironkova of Bulgaria on June 29.