Four years?
It's difficult for me to "admit" because I think you're oversimplifying. He's had three injuries. The unfortunate part has been the relative severity of each causing him to miss large chunks of games. Between the shoulder injury in junior and the knee injury last season, he played 66 games of 82. Unfortunately the knee injury and recovery took longer than it should have for some reason. We have no idea why. An ankle sprain is a fairly common injury. When you consider the freak, non-hockey play that caused it, it's hard to blame it on the kid (for some of us anyway). High ankle sprains are tough to return from. He tried and tweaked it again. We know from past experience that this injury can bother players for months. For all we know if the team were in contention, he could play through it.
Three injuries in three seasons doesn't really freak me out like it seems to most others, I guess. The severity is more bad luck than anything. It sucks, and it can't help his development, but I don't see any particular trend here when you really look at what has happened.
It's surprising to me how many make cracks about Murray, but no one mentions that Jenner's missed a lot of games for various injuries as well. No one seems to be lining up to call him 'injury prone' or 'made of glass' like some in these threads.
It's difficult for me to explain this in a way that I think you'll follow far enough to read this far, but this is the gist of it.