Garrett wrote on Twitter that he was driving when a fan hopped out of his vehicle to take a picture with the star defensive end. The Browns defender cracked the window for the picture before the fan gave him a "pillow tap" in the face.
"A 'fan' hopped out his car to take a picture with me and then punched me in my face," Garrett wrote. "Hm, put your legs into it might have actually made me flinch.
"Was in my car, flagged me down for a picture and I cracked the window enough for the camera to get my face. Took the pic and gave me a pillow tap."
Cleveland police identified a 24-year-old man they believe punched Garrett, according to Cleveland.com. No formal charges have been filed in the case, but police singled out the fan through his license plate.
The Browns, who completed their final bye week practice Wednesday, said in a statement that the "team is aware and the appropriate law enforcement authorities have been notified."
Garrett, the first-overall pick in the 2017 NFL Draft, is currently tied for the league lead with nine sacks this season. Through six games, he has 20 total tackles and one forced fumble.
After their bye week concludes, the Browns will play the New England Patriots on Oct. 27.