I am in the rare camp that really likes Maguire. All-in-all I think he seems like a really decent guy (and yes, I do know about Greece) and in spite of his poor form this season I think there is a good player in him too.
What is eminently clear to me, though, is that he is not ready to handle the pressure of the captaincy. Becoming the world's most expensive defender and moving from a relatively reputable side like Leicester to one of the world's most followed clubs is quite a heavy burden to start with, and it was then compounded by being given the captain's armband within about five months of joining. When you add to that the fact that we have since signed Edinson Cavani and Cristiano Ronaldo, two extremely well-respected senior figures within the game, it seems very likely that the level of pressure which comes with being captain of the team is not something Maguire is equipped to handle.