Coach Dave Cameron confirmed Friday that MacArthur's upper-body injury has been diagnosed as a concussion, Wayne Scanlan of the Ottawa Citizen reports.MacArthur's concussion stems from a collision in Monday's loss to the Hurricanes with teammate Robin Lehner, who was also diagnosed with the head injury and placed on injured reserve. Concussions typically result in volatile recovery timetables depending on the severity of the injury as well as the player's own personal history, so it's tough to speculate on when MacArthur's activation might come. In the meantime, he'll remain under the league's concussion protocol, keeping him off the ice until further notice.