Confidence cannot be bought, if he is getting in the right areas at youth level he will still do that at senior level. Some players are worth taking a punt on and i believe he is one of them especially considering we are low on strikers at the moment.
You can't compare youth and senior levels though, he could play a full 90 minutes in a senior game and do nothing just because the level of players involved jumps up a huge amount. Rafa doesn't need another reason for people to **** all over him.
That being said though, with the lack of depth Chelsea have, I'd throw him on against Brentford.