So apparently the story goes that Marlins pitcher Ricky Nolasco put down a squeeze bunt that dropped right in front of the plate that Geovany Soto chose to throw to first instead of third earlier in the game and Zambrano took that as a challenge.
His next at-bat, in the fifth inning, he tried to bunt himself on for a single and he stretched his left leg to beat the throw. Lou Pinella came out to pull him and Zambrano told him that it was just a cramp. Shortly thereafter he finally did leave, realizing it was worse.
Zambrano's status is pending an MRI, but Pinella said that he didn't foresee him making his next start, which, fortuitously, would be in Milwaukee Friday night. According to this artcie, the Cubs will likely have to pull up a minor league arm to fill the spot in the rotation.