The same injury had also forced her to withdraw from the Bank of the West Classic after winning her first match, and the Rogers Cup in Toronto.
“I arrived in Cincinnati yesterday eager to play. However, following the doctor’s advice on-site, as a precaution for the US Open, I am unfortunately withdrawing from the tournament with the left forearm injury I sustained in Stanford,” Sharapova said.
“I want to thank the tournament for the wildcard opportunity and really look forward to competing here next year,” she added.
The five-time Grand Slam champion was due to play French Open champion Jelena Ostapenko in a highly-anticipated first round clash.
Sharapova previously missed over two months of the season, including Wimbledon, with a leg injury suffered in Rome.
The injury cast more doubt over the Russian’s participation at the US Open, which starts in New York on August 28.
Due to her low ranking, the 30-year-old Sharapova would need a wild card to play in the main draw of the tournament.
Sharapova, banned after testing positive for heart drug meldonium at the 2016 Australian Open, has had mixed results since re-joining the WTA Tour. ( ANI)