I have to say, despite all the pumped flexed pictures the Barca admins are posting on a daily basis, it doesn't look like he has actually made that much physical progress at all from his start point.
I mean there are probably 5lbs more of muscle but nothing crazy like you would be led to believe from the reporting on his physical transformation. He looks like he only works biceps, still no shoulders or chest or anything.
I struggle to believe that if with the resources he has and at a club like Barca which has top sports scientists that he wouldn't gain significant muscle if he committed to it. Genetics and all yes but anyone can do better than that even with basic workouts.
Basically, I don't think that much effort is going into his physical work, or if it is, that he's doing something extremely wrong. It could be possible he isn't actually trying to build muscle and that they have determined his body composition is best like that.