Venus Williams withdrew from next week's WTA tournament in Montreal on Friday, citing an injured left knee that is hampering her preparation for the US Open.
The No. 4-ranked Williams already had pulled out of this week's hard-court event in Cincinnati, another warm-up for the year's last Grand Slam tournament, which begins Aug. 30.
In a statement issued by the Montreal tournament, Williams says she's looking forward to playing there for the first time, "but the pain that I am experiencing in my knee has unfortunately not gone away."
The seven-time Grand Slam champion hasn't played a singles match on tour since June 29, when she was upset in the Wimbledon quarterfinals by 82nd-ranked Tsvetana Pironkova of Bulgaria. Williams was seeded third for the Rogers Cup and her withdrawal caused four seeded players to be moved on the draw sheet. An extra player will make the main draw from this weekend's qualifying tournament. Play begins Monday.
If there are no further withdrawals, the tournament will have 40 of the top 45 players in the world. Williams' sister, No. 1 ranked Serena Williams, is also sidelined with an injury. The top seeded player is Jelena Jankovic of Serbia, followed by Caroline Wozniacki of Denmark, Elena Dementieva of Russia, Kim Clijsters of Belgium, Francesca Schiavone of Italy, Agnieszka Radwanska of Poland and Vera Zvonarova of Russia. The top eight seeded players have byes to the second round.
Former No. 1 Maria Sharapova of Russia is seeded 12th and will play Lucie Safarova of the Czech Republic in the opening round.