A frustrating season for Indianapolis Colts running backs got worse on Sunday when Marlon Mack left the field after suffering a concussion against the Miami Dolphins.
Andrew Walker of the team's official site reported the running back was ruled out for the rest of the game.
Mack found his groove after missing four of the first five games with foot and hamstring injuries. He had 347 rushing yards and four total touchdowns in three games from Week 6 to Week 8. His prolonged absence led to rookies Jordan Wilkins and Nyheim Hines receiving valuable experience earlier this season.