Monahan (lower body) has been ruled out for the remainder of Friday's game in Buffalo.
According to Aaron Portzline of The Athletic, Monahan exited the game after blocking a shot during the middle frame. The 32-year-old Monahan logged an even-strength assist and three blocked shots in 11:06 of ice time prior to his departure. The Blue Jackets' next game isn't until Tuesday versus the Panthers, so Monahan will have some time to recover for that matchup if his injury isn't overly serious.