Venus Williams has withdrawn from the Rogers Cup in Toronto due to a viral illness, the tournament announced.
"I was really excited to play Toronto," Williams said in a statement. "I came here ready to go and was practicing. I wasn't feeling very well and had to see the doctor today. I was diagnosed with a viral illness and unfortunately am unable to play. I am extremely disappointed."
As a result, qualifier Zhang Shuai will be replacing Williams in the draw and will play Ana Ivanovic.
The 31-year-old Williams has only played five tournaments in the past 13 months due to a variety of injuries including knee, hip and abdomen. She just returned to play after five months off at Eastbourne and Wimbledon, where she fell in the fourth round. It is unclear whether she will be well enough to compete in next week's tournament in Cincinnati, or entertain the idea of taking a wild card into New Haven.