Five-time Grand Slam champion Maria Sharapova withdrew Thursday from next week's WTA Rogers Cup tournament in Toronto with a sore left forearm, Tennis Canada announced.
The move came a day after the former world number one from Russia withdrew from the WTA event in Stanford, California, before a second-round match.
"I am so sorry to be missing the Rogers Cup this year," Sharapova said. "I am so appreciative to the tournament for the wild card and my fans in Toronto for their support.
"I am disappointed that injury is keeping me from the tennis court once again and I will work as hard as I can to return to the game I love as soon as possible."
The injury will cast further doubt over Sharapova's participation at the US Open, the last Grand Slam event of the season which starts in New York on August 28.
Due to her low ranking, Sharapova would also need a wild card to play in the main draw of the tournament.
Sharapova suffered the injury while playing in her first US match in more than two years, defeating American Jennifer Brady 6-1, 4-6, 6-0 in her Monday opener at Stanford.
She had not played in the US since March of 2015 due in part to a 15-month doping suspension for the use of meldonium.
"Toward the end of the Monday night's match, I felt pain in my left forearm," Sharapova said Wednesday. "After yesterday's scan, the doctor has recommended I don't risk further injury."
Canadian 17-year-old Bianca Andreescu will receive the wildcard entry vacated by Sharapova.
"We wish Maria the best and hope she is able to return to the court 100 percent healthy soon," said Karl Hale, Rogers Cup Toronto tournament director. "We know many of our fans were excited to see her play."