It was a scary scene in Columbus when McDavid left with the injury. Looking at the injury in slow motion, McDavid jammed his ankle into the boards incredible awkwardly. He was able to skate to the bench, but with injuries like those, the major concern is structural damage that could hold a player out for months.
There hasn't been an official confirmation of the injury, but most sources believe that McDavid suffered a low-grade high ankle sprain. Typical recovery time is between 1-3 weeks, so it's very possible that McDavid could make an early return. It was projected he may miss 6-11 total games, so hopefully, it's closest to just 6.