Williamson left Tuesday's game against Atlanta with a left elbow strain, Charlie Goldsmith of The Cincinnati Enquirer reports.
Williamson suffered the injury after throwing a pitch in the second inning of Tuesday's contest and had to be taken out of the game immediately afterward. The Reds haven't specified the severity of his injury, but if the team elects to place the left-hander back on the injured list, his season would be put to an early end after just four starts.