At risk of being attacked by anyone who doesn't think we should be realistic about our youth options, has he done anything yet to suggest that he's ready for that? In a cup game with a strong team around him, fine. In the league or CL, any decent senior defender will be able to snuff him out quite comfortably. I think for now Díaz is best utilized either in easier games to gain experience or against tired legs as a substitute. I'm not saying he'll never be good enough, just that for now I think Bernardo, Sterling or Zinchenko would all be better options on the left.