Or maybe he's just going through a bad patch? Just because Messi hasn't show any signs of form in his career doesn't mean that the level of his performances can't vary. Bit of a hyperbole to talk of decline, losing x qualities etc after a few months of sub-par performances, sub-par by his level that is, especially when the tactics we play really don't suit him or the team as a whole.
He was out of form the last month or so, sucks but it happens to every player, also there have been plenty of games this year (City return game, classico at the Bernabeu, Osasuna game, Getafe games when he just came back) to show that everything is still there skillwise so it must be more of a mental thing.