Ostlund sustained a lower-body injury in the first period of Game 5 versus the Bruins on Tuesday and will not return.
Ostlund appeared to be favoring his left leg after a collision with Casey Mittelstadt. The 22-year-old Ostlund attempted to skate it off during a TV timeout, but he was unable to stay in the game. The silver lining is that this injury isn't related to the upper-body injury that recently cost him 12 contests before he made his playoff debut in Game 3 of this series. He'll be day-to-day until the Sabres provide additional information.