It happened as he tried to beat out a double play at first base in the bottom of the 4th and it immediately didn't look good. Francisco Cervelli grabbed at his right hamstring and collapsed to the ground after crossing the first base bag, and he just limped off the field and straight into the locker room. At best, he tweaked the hamstring similarly to how Mark Teixeira did last week. It looked a lot worse than that though, and the Yankees are really, really short on healthy infielders right now.
Kelly Johnson will probably have to move to 1st base for the rest of this game and Joe might have to play Jeter at short. This situation gets worse and worse. More on this story as it comes out.
** UPDATE 8:38 PM- Joe confirmed on the ESPN broadcast that it was a right hamstring injury for Cervelli. Carlos Beltran has come in to play first base for the first time in his career and Ichiro will go to right field. Check the live blog below for any more updates. **