How to spot the old curmudgeon in the room....
Sorry, leadership/management 101. Can't expect your subordinates to improve or fix their mistakes by not communicating with them. Takes 10 seconds to say "Hey Kaap, love you kid but we need more from you if we are going to go anywhere. You are sitting this game for fresher legs"
Bam, done. Now he knows where he stands and now the onus is on the player to light a fire under his ass. As opposed to saying nothing, it could feel personal and not performance based. Then the player has an open door to "why should I give a f*** if he doesn't give a f***"