While going for a loose ball the back of Drummond's head smacked into the side or hip area of Roy Hibbert and Drummond definitely got the worst end of that collision. Drummond instantly sprawled to the floor holding the back of his head. He stayed down for several minutes and had to be helped off the floor.
At halftime the Pistons officially announced that Drummond suffered a neck injury and would not return.
There's not indication whether the injury will be long term, but the fact that the team has officially said it is a neck injury means it less likely to be a concussion. If it were a concussion then Drummond would have to pass a series of tests and could be held out for an indefinite amount of time.
We will provide more information when we learn more.