Max Scherzer left the Texas Rangers' 6-3 win over the Blue Jays in the sixth inning on Tuesday night because of a right triceps spasm.
He is set to undergo an MRI on Wednesday.
Scherzer didn't allow a run before exiting and snapped a four-start winless streak. He threw 73 pitches, 49 for strikes.
He began feeling tightness while warming up for the sixth and hoped it would pass.
"When I threw that first curveball to [Bo] Bichette, it just felt like a charley horse," Scherzer said.