According to ESPN, an exam with Dr. James Andrews revealed that Posada's shoulder injury is likely not season-ending. It mentions (again) that if it is just a strained shoulder, he will not need surgery.

Either way, I'd be very cautious about this. This seems like the same thing that was being said a couple weeks ago when they started DH'ing him. There's obviously something wrong with his shoulder if it's been this much of a problem already. Better safe than sorry.