If you'll recall, Chris Carpenter has been out of action for a very long time. He's very slowly been building himself back up, and Monday he was set to throw to hitters. If that throwing session went well, the Cardinals thought about sending him on a minor-league rehab assignment. Carpenter hasn't been close to coming back, but he's been making progress.

Unfortunately, Monday's throwing session didn't go well, in that it didn't go at all.

Carpenter will not face hitters today as scheduled. Felt "weakness," per Matheny. Will have schedule set when #Cardinals return home.

— Derrick Goold (@dgoold) June 25, 2012

So this is a setback of unknown severity. Based on the reaction, it isn't thought to be terrible news, but it's unwelcome news that pushes back Carpenter's expected date of return. He'll throw soon, and in the meantime the Cardinals will do their best to remain in the race with a depleted rotation. Kyle Lohse posting a sub-3 ERA certainly doesn't hurt.