i love marchisio (he's my fav player of the current bunch), and probably max does, too. i mean marchisio was a dead starter for juve before his injury. but i have no idea about his physical condition, and even if i had, i wasn't qualified enough to assess whether he's match fit, and i never followed him on training either. so i fully trust allegri when it comes to player selection. when marchisio is - rarely - selected, his passing looks all right, his speed is lacking, and he never challenges opposition players for balls the way he used to. for me, he looks like a softer version of himself. it's either match fitness, or he's just trying to save himself some knocks, bruises and potential injuries, which is understandable from his point of view.
i suppose there's nothing to see here, he's probably done as a professional footballer at this level. we'll see whether he moves in the summer. in case he's still useful, even for some 800-1000 minutes per seasons, the club has no reason to sell him, though.