McHugh (arm) called for the trainer and exited Thursday's rehab start after just one inning, The Fresno Bee's Bryant-Jon Anteola reports.
He gave up three runs on three hits and a walk while throwing 27 pitches in the first inning, but after going out to the mound to begin the second, he exited with the trainer before throwing a pitch. McHugh will need at least one more rehab start after failing to build up his pitch count Thursday, and if he has indeed aggravated the injury he may be out of the big-league rotation indefinitely.