#3 Fitness
This is a criterion where the Senegalese is even better than the Dutchman. Koulibaly has missed just 12 games due to injury in his entire career! That is just 12 games in over eight seasons!
Even though it sounds unbelievable, the Senegalese has played over 300 games in his career so far and has largely remained injury free. Considering how susceptible to injury the Manchester United back four has been in recent years, Koulibaly looks like an immediate upgrade in this regard as well.
The Senegalese's first major injury was a Metatarsal Fracture endured during his days as an FC Metz player. He was sidelined for 44 days, a span where he missed seven games between April and May. That was in the 2011/12 season!
Koulibaly has been injured twice while playing for Napoli. In the 2014/15 season, he was out for a week with a knock and missed two games. In the 2016/17 season, he sustained a sideband strain in the knee and was sidelined for 15 days, where he missed three games.
As such, with his ability to stay fit, the Senegalese could be the perfect man to solve United's defensive woes.