St. Louis Cardinals starter Carlos Martinez was removed with right shoulder tightness after throwing seven pitches in the first inning against the Milwaukee Brewers.
The 14-game winner flinched after making the first pitch to Adam Lind, the Brewers' third hitter.
After meeting with trainers and manager Mike Matheny on the mound, Martinez left the field with his glove covering his face and in apparent pain.
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The team said the 24-year-old Martinez would be evaluated Saturday.
Martinez entered with a 3.01 ERA in 31 appearances (29 starts) this year for the Cardinals, who have already clinched a postseason berth.
Tyler Lyons replaced Martinez. Lyons has made seven starts.