Stastny appeared to collide with Maple Leafs forward Nazim Kadri shortly after the face off at center ice to start the second period. He went to the bench where he remained for several minutes of action but at a stoppage in play, returned to the locker room.
Stastny did not return to the game due to a lower-body injury.
Blues Head Coach Mike Yeo said Tuesday that placing Stastny on injured reserve will keep him out of the lineup for Wednesday and Thursday's games, but he hasn't been ruled out for Saturday's game against Buffalo.
"He's usually the first guy over the boards for a power-play face-off or the first guy over the boards for a penalty kill faceoff and those are key. He's a very important player for us," Yeo said. "You don't take out a top-line center from too many lineups where they don't feel that. It's got to be a next-man-up mentality here. We have more than capable players and our focus is on the guys that are in the lineup and if we take care of our job, we give him a chance to get better and obviously we'll be stronger when he gets back."
The 31-year-old forward ranks fourth on the club this season with 35 points (15 goals, 20 assists).
