Five on the court, one is injured

[potato]

Is there any medic on the scene that can determine whether an injury is deemed serious that the player should not be allowed to continue to play?

If there isn't, then it's up to the coach & player to determine whether if a player is fit to play and the ref should decide whether to allow the player to continue.

I mean if the player rolled the ankle but can still stand and move around, it would still be better to put the player at the defensive side so while the team is facing 4 on 5 on the offense, they'd still have 5 players on the defense.