Judging by the lad's twitter, he has been training with the team since 4th Jan. It is a bit annoying from the fans' perspective that we haven't seen him yet or had any official unveiling. But I reckon there's method behind this by Pep. Let the guy settle in in England and get up to scratch away from all the media hype, who will be quick to build him up then knock him down again if he doesn't bag a goal every game. They did it with Robinho, and he had tonnes more experience in the game when we signed him, than this lad.
People forget, he is 19 years old and would not surprise me if this is the first time he's ever been on a plane outside of South America. Give it time, he has the right management and people around him at City. Pep will put him out there on the pitch when he sees fit, and give the green light for any media.