#3 Juan Mata

Now, now, calm down.
Nobody is saying that Juan Mata isn't the nicest guy in world football. Nobody is saying that Juan Mata isn't one of the loveliest footballers to watch when on song.
He is, though, hopelessly ineffective when things start getting even a bit physical and... as astoundingly blunt as this sounds... lacks the upper-body strength to be able to compete effectively with the increasingly more powerful opposition.
He also requires a whole lot of the ball to be able to make some impact on games - but is simply not good enough to build a team of United's ambitions around, or to obtain the status of "luxury player" , one with the license to do anything without having the responsibility to hold position or trackback.
As hard as this is to read, and to write may I add, Juan Mata is just not good enough to play the role he seeks for a team that wants to win every competition it competes in.