The Red Sox placed Paxton on the 15-day injured list Monday with a right calf strain, Jen McCaffrey of The Athletic reports.
Paxton suffered the injury during Sunday's 10-2 loss to the Astros and required assistance off the field. The southpaw was scheduled to undergo an MRI on Monday, but the severity of the calf strain has not yet been revealed. The Red Sox are likely to turn to either Josh Winckowski or Cooper Criswell (COVID-19 injured list) to serve as their new fifth starter in place of Paxton, who is first eligible to return from the IL on Aug. 27.