Shelby Miller left the Arizona Diamondbacks' loss to the Los Angeles Dodgers on Sunday after just four innings because of right forearm tightness.
Miller threw four shutout innings before walking two batters and giving up an RBI double. He threw one more pitch, then left after a visit to the mound by the Arizona trainer.
He will have a precautionary MRI on Monday.
Torey Lovullo said he got a signal from an Arizona player that something wasn't right and made the decision to remove Miller from the game.
"These are tough things for me to address. It is really unfortunate," Lovullo said. "Shelby has been throwing the ball really well. This is a minor setback for him but, numbers aside, you just hate to have a situation like this pop up."