Send him on loan in the PL next season, call him back in January. If he's doing good add him to the squad if not send him to the championship. To play a guy that young in a position of such influence is very risky. Regardless of if he's good enough that position is there to provide confidence to the back 4 and the front 4-5 that he'll keep it safe and tight. With a player like Chalobah just the simple fact that he's 18 and inexperienced at the top level will always force Luiz and others around to keep him in their peripherals and almost try to spoon feed him. He needs to learn some things the hard way, make some mistakes at a team where one mistake won't relegate you to the bench for the rest of the year. He makes one bad mistake in his first game, he's instantly third choice at Chelsea behind Mikel and Romeu, then wait till a Carling Cup game to maybe get that spot back.