Maria Sharapova has withdrawn from the Cincinnati Open with a nagging left arm injury she suffered during competition earlier this month, the former champion said on Sunday.

Sharapova, who suffered the injury during her first-round match at the Stanford Classic, said her decision to withdraw from the Cincinnati event, which granted her a wildcard, was a precaution ahead of the year's final grand slam.

The 2011 champion said she arrived in Cincinnati on Saturday eager to play but following the doctor's advice on site decided to withdraw from the US Open tune-up, where first-round action begins on Monday.

Sharapova was scheduled to play French Open champion and world number 12 Jelena Ostapenko in a highly-anticipated first-round clash.

The Russian's decision to withdraw marks the latest setback in her comeback this year after a 15-month doping ban.

Sharapova, banned after testing positive for the heart drug meldonium at the 2016 Australian Open, has had mixed results since rejoining the WTA Tour.

The 30-year-old reached the semi-finals as a wildcard in Stuttgart, fell in the second round at Madrid and retired from her second-round match at the Italian Open in mid-May after injuring her left thigh.

After pulling out of Stanford, Sharapova withdrew from the Rogers Cup in Toronto.

The arm injury casts a cloud on Sharapova competing in the Aug. 28-Sept. 10 US Open since the former world number one would need a wildcard to compete in the event.