There's video of it on Puck daddy. He makes a save and kind of lunges over to his right with his upper body, while still in the butterfly. Something he's probably done 5,000,000 times (I'm a goalie, you do what he did all the time lol). It just looks like he tweaked something, I would say MCL or Hamstring from the way he looked getting off the ice.
I tore both my left and right MCLs while in my sophomore and then junior seasons at college. Both times it was making movements that I'd done thousands of times. It wasn't a dramatic awkward dive either time. First time it was a save in the butterfly, then I shot out my left leg into a split and fell forward towards the puck, and I tore the MCL. Second time, my right one, all I did was go down into my butterfly on a routine save (shot from the point with no screen). Both times, nobody had any idea I was hurt because I simply made movements I make hundreds of times in a single game.
I guess my point is that he could've torn something bad enough to keep him out even doing something as simple as a routine save.