Winn was removed from his start during the fifth inning of Tuesday's game against the Dodgers due to right forearm tightness, Alex Pavlovic of NBC Sports Bay Area reports.
Winn will receive an MRI on Wednesday, at which point more will be known regarding the severity of his injury, as well as a potential return timeline. The 26-year-old righty allowed five earned runs through four-plus innings before getting pulled and is tentatively lined up to make his next start Sunday against the Rockies.