Legace has a dislocated knee cap. Having had the same injury years ago, it's something that I still suffer from today. If it's a serious displacement, he's not coming back anytime soon, if it's a minor with little tissue damage he might be back and playing gingerly in about ten days.
Fluery is also injured but should be playing again shortly.
If you can afford to wait on Legace's return - and it could be awile - then it's probably a good idea to drop Fluery, then grab Legace and put him on IR and then pick-up Fluery again. That way you'll have Fluery in your roster until Legace is back from injury.