Deschamps does that because he doesn't want to bring attention to the issue, as it may affect the team. For example, whenever Cassano doesn't play, he makes a big fuss, and Capello tries to fix things. That's not the best approach, as the media just feeds off of it and makes transfer rumours regarding the player. It's best to just brush it off and tell the player to keep "his head clear" so the player knows that he has to be ready anytime he's called upon. Smart coaching on Deschamps' part.