According to Cardinals GM John Mozeliak, Chris Carpenter is expected to miss more than two months thanks to a nerve issue in his neck and pitching shoulder.
Carpenter reporter pain in his neck and weakness in his shoulder before he could make his first Grapefruit League start in 2012. He had it checked once and doctors thought it was a bulging disc. But after re-starting his throwing program, he suffered weakness in his shoulder and pitching arm.
This is likely related to the nerve problems Carpenter suffered in his pitching arm in 2009 that were considered at the time to be career threatening.