#1 Leadership skills
Manchester United do not have a leader in the back. They immensely miss a player of the caliber of Virgil van Dijk, who can arrange his defense and push his men forward to thwart the opposition pressure. They need someone to bark orders, someone with just the right amount of aggression and steel to lead the team when in distress and it is hard to look at anyone other than Kalidou Koulibaly in this regard at present.
The Senegalese is the defensive stalwart at Napoli and hardly lets anything distract him. His confidence and his abilities make him a natural leader on the pitch and Koulibaly has been regularly seen addressing his defense and roughing his men up when they are slow to react.
He has the ability to push his men, to inspire them and direct them from the back. Even under intense opposition pressure, Koulibaly has a very cool head on his shoulders. In addition, he has a fantastic understanding of the game and his mental steel is exactly what United need right now.
If the Senegalese joins United, the Premier League side will be getting a man of character, a man with the right attitude to fix their faltering defense.