Head injury and neck injury
Unconscious players cannot tell you if they have a painful or tender neck. We know that significant head injuries occasionally have an associated neck (cervical spine) fracture. Anyone who is unconscious from a head injury or complains of neck pain needs to be considered to have a serious neck injury. Further unnecessary movement can turn a bony neck injury into a paralysing spinal cord injury, so protection of the head and neck through manual in-line stabilisation (MILS) and discouraging the player to move it is a key skill.
Time is our friend and after a short while of simply protecting the neck with MILS and making an assessment of DR ABC, the player may regain consciousness and be able to tell you he does not have a neck problem, allowing you to release MILS. If there is any doubt, however, MILS should be maintained. All players who are knocked out should be removed from play, not left alone or drive a motor vehicle and be reviewed by a doctor as soon as possible.
If there are any concerning symptoms such as neck pain, weakness, difficulty breathing or altered sensation in the limbs, or the player is obviously confused or unconscious, then you should maintain MILS and monitor ABC until more experienced help arrives.