relaying from the game thread....but Chris Kuc said on twitter "not serious"
keep those fingers crossed.
He was walking which is good but you never know with a hockey player. Sounds like a sprain, if mild should be 1-3 weeks based on my personal experience.
If MCL and more severe, as the angle of the hit could cause the knee to buckle inward, it could take time for him to feel stable without one (common rugby injury due to tackling restrictions.)
I didn't feel right for about 14 months but mine was the most severe you can get without needing surgery, which occurs when the mcl pulls the bone its attached to with it. If it just snaps your ok