Johnson exited his start with Triple-A Pawtucket on Saturday due to a hamstring cramp and will be reevaluated Sunday, Pete Abraham of The Boston Globe reports.
Initial reports were that he had left the game with a calf strain, but it's concerning news for the Red Sox nonetheless. Johnson was poised to be a prime candidate for a start against the Tigers next Saturday -- the next time a fifth starter is needed -- but those plans will be put on hold until he can be reevaluated by trainers. The southpaw has a solid 2.57 ERA and 1.07 WHIP over two big-league starts this season.