3.10 If the referee decides – with or without the advice of a doctor or other medically qualified person – that a player is so injured that the player should stop playing, the referee may order that player to leave the playing area.
I have always understood that this gave the referee the final word, whatever a medical person may say. After all, that person is not neutral.
At a relatively low level game, I once saw a player knocked out, and after he came round he was helped off the field, looking in a pretty bad way. Nonetheless 20 minutes or so later he wanted to rejoin the game with the insistence of the club physio that he was fit. The referee refused to allow him back on, and after the match was immediately subjected to some fairly unpleasant criticism from club officers.
I noted the incident and decision in my report, strongly supporting the referee.