3.8 THE DECISION FOR PERMANENT REPLACEMENT

(a) When a national representative team is playing in a match, a player may be replaced only when, in the opinion of a doctor, the player is so injured that it would be unwise for that player to continue playing in that match.
(b) In other matches, where a Union has given explicit permission, an injured player may be replaced on the advice of a medically trained person. If none is present, that player may be replaced if the referee agrees.