This is such a myth. The three seasons since he left us he played 34, 37 and 31 games, including a season as a first choice in Barcelona's midfield.
He's nowhere near match sharpness because he is not only lacking a preseason but also the rest of the squad (and the league) were more than 10 games in before he even set foot on the pitch.
He ain't gonna be the best midfielder in the league, but he will get up to sharpness and be an excellent asset for us. He won't have lost his physical strength and his greatest asset beyond that was his anticipation and reading of the game, which again he won't have lost - he'll just need time on the pitch to hone it.