His performances for Manchester United suggest that he has the potential to become world class. I still think Fábio is technically better than Rafael, he's certainly a better dribbler and passer IMO. He's not a top player just yet, but what makes me think he'll reach this level is his performances in 10/11. He played really well in the UCL, against the likes of Rangers, Marseille, Schalke, and even Barcelona - we're talking about a very talented player who has already proved that he can play in big games. Fergie played him in several crucial games that season, towards the end. He played in four of our last five fixtures, if I remember correctly, against Everton, Arsenal (our best player), Chelsea, and Blackburn.
Moyes playing Buttner is baffling because we have a better player in Fábio. Moyes playing Smalling and Jones at right back is also baffling because we have a better player in Fábio... And when he plays as a right back, he's not really out of position.