Posada was replaced at catcher by Francisco Cervelli before the sixth. Manager Joe Girardi said Posada's calf started bothering him during his second at-bat, as if someone hit him in the leg. An MRI revealed a mild strain, and the Yankees said he was day to day.
"My guess is we'd be without him for a couple of days," Girardi said before the test results came back. "He'd be an emergency catcher, so maybe you're looking at Friday again."
Posada missed two straight starts last week with a swollen right knee after he was plunked by a pitch from Baltimore pitcher Jeremy Guthrie, who also started Monday night's game.
Information from the Associated Press was used in this report