An MRI taken yesterday revealed a torn capsule in his throwing shoulder. His arm will be in a sling for three weeks, after which period he'll have another MRI.
The capsule is a tissue layer that provides stability to the shoulder. When torn, there is a loss of range of motion, and it becomes extremely painful to move the arm. Treatment can be simple, with measures taken to reduce inflammation and exercises performed to strengthen the surrounding muscles. Over time, range of motion may gradually return as the stronger muscles begin to adequately stabilize the shoulder. However, if the pain continues and the shoulder doesn't show improvement, surgery may become necessary to repair and strengthen the torn capsule. In this case, rehab can take a while.
Best-case scenario is probably having Bobby back in the rotation in 6-8 weeks. The worst-case scenario is a lost year. Until we have an idea of the extent of the tear, we can't really say how long he'll be out of action.