What do you do when you suspect a player is seriously injured? The answer is easy. Just stop the game. In the video below, the player is hurt but at first, it is not very clear how seriously she was hurt. Fortunately, the ball goes out of touch and the game is stopped. The referee correctly identified that the player needed some assistance.
Oftentimes players go down because of collision. But some other times, they may go down without any apparent contact from another player. The latter case, even though there was no contact, could be serious. There are times when the situation is more serious when a player goes down alone than because of contact from an opponent.
So if you see a player go down without any contact from another player, be extra cautious. The player may need assistance more than we imagine.