Muzzin, like Martinez, is a bubble player. He has a very hard slap shot that makes him lethal on the powerplay, but his all around play has been below average, where he was called out by Sutter, saying that he has to play a hell of a lot better to be partnered with a special player like Doughty.
There isn't a defensive prospect who is actively challenged to make the line-up in his place, right away... if that helps you at all. But he was recently called out and in the grand scheme of things, is a little lower on the depth chart.