If Mourinho wants him, he's probably a good signing even if he isn't a player that deserves/can't play week in, week out. His leadership off the pitch and ability to influence would be helpful. He's in between a luxury player and a necessity in my mind. Prior to the "reSergence" of Aurier, he seemed to be a good fit given the price that has come out, but if Serge is born again, then it probably makes sense to spend on DM and LB above all else. And that is a qualified "if".