On February 16, 2015, MacArthur collided with goalie Robin Lehner, resulting in both players being diagnosed with concussions. On October 20, 2015, Senators general manager Brian Murray announced that MacArthur suffered another concussion during a game against the Columbus Blue Jackets on October 14 and that MacArthur would not be playing in the near future. MacArthur played only the first four games of the 2015-16 season due to his concussion, although he passed a "baseline test" and was announced to be "medically cleared to play" in late March 2016.