#4 His leadership qualities
Ever since Sir Alex Ferguson's retirement and Wayne Rooney's departure, Manchester United have lacked a leader on the pitch. Someone strong, vocal, a man who leads by example. Right now, Ander Herrera is that man on the pitch, the one binding the team together.
The Spaniard has been used in various capacities ever since arriving at Old Trafford and has almost always yielded results. Perhaps the biggest reason for his success has been his ability to carry out instructions.
Under Louis van Gaal and Mourinho, Herrera had been cast aside but had clawed his way back into the team, simply because there are few men in the league who can carry out a job like him.
The Spaniard is a very responsible player on the pitch and if utilized efficiently, has the ability to inspire the team. He is the unsung hero on the pitch, someone who does not hog the limelight yet does some of the most important work for the team. United cannot afford to lose such a player.