Williamson was removed from Wednesday's game against the Rockies with left shoulder fatigue, Charlie Goldsmith of Fox 19 Now Cincinnati reports.
Williamson made it through just three innings before coming out of Wednesday's game, giving up four earned runs on four hits and four walks while striking out four batters. It's currently unknown whether the shoulder issue will cause the Reds to postpone his next start or move him to the IL, but he's slated to receive an MRI on Thursday that will help determine his short-term availability.