I'd be pretty damn surprised if he has the quicks to play fullback. You look at the best teams in the world and the slowest starting fullback is Ivanovic, and he's actually pretty quick and powerful once he gets going. I guess Lahm is slowing down too, but he's so good on the ball it's criminal. Alaba, Bernat, Felipe Luis, Azpilicueta, Zabaleta, Clichy, Alves, Alba, Carvajal, Marcelo and the others are all quick enough to threaten on the overlap.
He's very good on the ball, though, so hopefully he can be a CB here. Definitely an intriguing prospect.