In the event of a suspected concussion, the referee stops the game to allow the injured player to be assessed by the team doctor, in accordance with Law 5 of the IFAB Laws of the Game. In principle, this should take no more than three minutes, unless a serious incident requires the player to be treated on the field of play or immobilised on the field for immediate transfer to hospital (e.g. spinal injury).
Any player suffering a head injury that requires assessment for potential concussion will only be allowed to continue playing after such an assessment, upon specific confirmation by the team doctor to the referee of the player's fitness to do so.