Montgomery left his start Friday versus the White Sox due to a right hamstring injury, Jeff Jones of the Belleville News-Democrat reports.
Montgomery appeared to tweak his hamstring while delivering an errant breaking ball to Elvis Andrus in the bottom of the fifth inning and promptly departed the game. He wasn't going to pitch again until after the All-Star break either way, but the Cardinals will place him on the 15-day injured list if the injury requires multiple weeks of rest and rehab. The 30-year-old left-hander has been shaping up as a possible trade candidate for St. Louis in the final year of his current contract, holding a 3.23 ERA, 1.22 WHIP and 96:27 K:BB in 18 starts covering 103 innings.