Treanor pulled up immediately after he lined a crisp single to left field off Cardinals right-hander Anthony Reyes. While sprinting out of the batters' box, the catcher buckled, reaching for his leg. He hobbled to first and was observed by assistant trainer Mike Kozak.
Treanor said he was previously experiencing some tightness in his left calf.
"I felt it a little bit earlier, I had been stretching," Treanor said. "I think it might be a pretty good cramp. It's been sore for a while."
Paul Hoover pinch-ran for Treanor, who limped back to the dugout. By the top of the fifth inning, the catcher walked slowly to the team clubhouse.
Treanor most likely will miss at least two days. He wasn't scheduled to travel with the team to Viera, Fla., on Thursday night to face the Nationals. Now he will get treatment.
"With the heat and stuff, I hope a cramp is what we're looking at," Treanor said.
Treanor and Mike Rabelo are expected to split the catcher role, with the breakdown in playing time being pretty equal.
Joe Frisaro is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.