The muscle isn't damaged, it's that the nerve is not telling the muscle what to do:
"The 21-year-old goaltender drafted to be the heir to Mike Richter's net learned at his last neurological exam that the damaged nerve in his injured left shoulder has not recovered sufficiently. And as it has now been 16 months since he suffered the original injury and nine months since the speculative surgery that only partially solved his problem, doctors fear that Blackburn never will regain full use of his left arm for goaltending purposes.
Specifically, the damaged nerve in Blackburn's shoulder governs the movement of two important muscles in his left arm. The nerve has healed completely in its ability to fire one of the muscles but not the other - the muscle that allows him to snatch up his left hand quickly enough to catch pucks shot by NHL players."
http://www.nydailynews.com/sports/hockey/story/268991p-230350c.html