Rst - Match fit but starting to get jaded

For the first time in all of my FM years I have seen this description in one of my player's profile. He needs a rest, obviously, but how dangerous would it be to keep on playing him in terms of injuries and development? He is only 20 but one of the best players at the club and up next is the important second leg of the Europa League quarter final.

I've personally never started a player with the Rst sign. But I cant imagine it doing too much harm just rest him for the game after if he still needs a rest.