By the sounds of it he's extremely talented and was considered one of Sporting Lisbon's best prospects but fell out with the coach and ended up getting loaned out. From what I can gather he was expected to start the season for them last year after a very bright pre-season but was on the bench the first game, made a tweet complaining about it, and was banished on loan.
Seems like he's got attitude issues but also a lot of talent. Hopefully Bilic is the man to rein him in and get the best out of him.