It is now down at 171 following a 15-month doping ban which ended in April and her thigh injury which occurred just weeks into her comeback in Rome.
It is not known how long the injury will sideline Sharapova for but she is due to compete as a wild card in the Rogers Cup in Toronto next week.
"At the end of the match against Brady I felt the pain in his left hand".
Sharapova made her return to the WTA after eight weeks away with a leg injury on Monday in Stanford, where she defeated Jennifer Brady, 6-1, 4-6, 6-0.
"I am so sorry to be missing the Rogers Cup this year", Sharapova said. I am very grateful to the organizers for giving me a place and to the fans for the support they have always offered.
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 NY on August 28.
Citing left arm soreness, Maria Sharapova has withdrawn from the Bank of the West Classic in Stanford. After yesterday's scan my doctor has recommended I don't risk further injury.
Sharapova was denied a wildcard for the French Open and missed Wimbledon, where she was going to try to gain main draw entry through the qualifying tournament, due to injury. This was the first WTA tournament she had played in the United States since 2015.
"We wish Maria the best and hope she is able to return to the court 100 per cent healthy soon", said Karl Hale in a press release, Rogers Cup Toronto tournament director.