Which action must a referee take if a player is injured and cannot continue?

When a player is injured and cannot continue, the appropriate action for the referee is to stop play to provide medical assistance. This is crucial for the safety and well-being of the player. Stopping play ensures that any necessary medical attention can be given promptly and that the player's condition can be assessed properly.

Moreover, prioritizing player safety is an essential part of the referee's responsibilities. An injured player should not be left on the field without assessment, as this could exacerbate any injuries they have sustained. Stopping play allows for an immediate reaction to the injury, ensuring that medical staff can enter the field without risk to the player or the progress of the match.

In contrast, allowing the player to walk it off or continuing play if the injury is perceived as not serious could lead to further risk of injury. Additionally, waiting for a substitute while a substitute is not immediately available fails to address the urgent need for medical attention that an injured player requires. Thus, stopping play to provide medical assistance is the correct course of action that aligns with the priorities of player safety and game integrity.