It hasn't been confirmed when the injury occurred but Carter Brooks of Sports Illustrated shared the following about the situation.
As you can clearly see, Scheifele could barely muster a shot from the faceoff dot while the Jets were on the man advantage in the first period, and he immediately left the ice afterward.
During the first intermission, Sportsnet's Elliotte Friedman confirmed that Winnipeg will not get their number one centre back tonight against the Golden Knighs.
It's being reported that Scheifele suffered the injury early into the game, when he crashed hard into the end boards - shoulder first - after a partial breakaway.
When looking closer, it appears that Vegas goalie Laurent Brossoit gets his stick into the forward's feet: