The 26-year-old former world no.1 complained of dizziness after the smash, although his air bag saved him from any serious external injuries.
Bad luck has cursed Safin in Cincinnati as he picked up a serious knee injury at a tournament in the U.S. city last summer, which sidelined for almost six months until this February. The Russian was forced to miss last year's U.S. Open and was unable to defend his Australian Open title.
The injury also appeared to affect his game and confidence, which led to him plummeting to 74th in the world rankings.
At this week's $2,450,000 Cincinnati Masters tournament Safin lost to France's Gael Monfils in the first round of the singles, and lost in the doubles quarterfinals Thursday with compatriot Mikhail Yuzhny.
Safin began his professional career in 1997 and was world No.1 for nine weeks in 2000. He helped Russia to win its first Davis Cup title in 2002, with a 3-2 tie-breaking victory against France in the final in Paris.
Safin has two Grand Slam to his name: the 2000 U.S. Open and the 2005 Australian Open.