Williamson was placed on the COVID-19 injured list and won't start as scheduled Sunday against the Cubs, Charlie Goldsmith of The Cincinnati Enquirer reports.
Williamson joins Hunter Greene, Ben Lively and Fernando Cruz as Reds pitchers on the COVID list. No replacement starter has been named for Sunday, but Connor Phillips, Michael Mariot and Levi Stoudt are potential options to be called up from Triple-A Louisville.