She returned to competition in April, but her comeback has been disrupted by a hip injury that forced her to withdraw from Wimbledon qualifying.
"I am so sorry to be missing Rogers Cup this year", Sharapova said in a press release. The injury casts a bigger cloud on Sharapova competing in the year's final grand slam, with the former-world No. 1 hoping for a wildcard into the US Open, an event she won in 2006.
Having missed the entire grass-court season, the five-time Grand Slam champion will not gain direct entry into the US Open, which starts on 28 August.
Five-time Grand Slam champion Maria Sharapova made a battling return to U.S. hardcourts on Monday with a 6-1, 4-6, 6-0 victory over American Jennifer Brady in Stanford, California. The former world number one from Russian Federation hadn't played in the United States since March of 2015. After yesterday's scan my doctor has recommended I don't risk further injury.
The absence of Sharapova opens the door to the main table to the young canadian Bianca Andreescu, who had been offered an invitation to the round of qualifications.
"This is definitely tough for Maria", said Bank of the West Classic Tournament Director Vickie Gunnarsson. "We know many of our fans were excited to see her play".
She had been scheduled to play Wednesday night, so seventh-seeded Lesia Tsurenko moves on to the quarterfinals.