I'll bet on an injury. Otherwise he would at least have fought one time, right?
But still, again, people should stop overestimating the players they like. Prust has never been anything else than a fourth liner. He played great last year in a shortened season, but still finished with 4 goals.
Now I do think he's the PERFECT fourth liner since he can be used on other lines on some occasions and he can play on the PK, but still, we're talking about a fourth line player.
Don't forget that while everybody were happy to see Habs sign such a player, the majority of observers tought at the time that it was overpayment nonetheless. So we shouldn't hope for too much of him. If he becomes such a key player for victories, then it would mean Habs are in trouble.