#2 Kalidou Koulibaly (Napoli)

Kalidou Koulibaly is a 27-year-old centre-back who currently plays for Napoli in Serie A. While he began playing for France's U20 side back in 2011, he eventually opted to play for Senegal instead, having played 31 games since making his first team debut back in September 2015.
Koulibaly has been linked to a plethora of top clubs over the past few transfer windows, but with him now in the middle of his peak years, a team that wants him must make this summer the time to sign him, before it's too late.
Imagine the impact a player like Koulibaly would have on United's defence; there would certainly be no more worry insofar as who might play alongside Lindelof in the centre-back role. Another strong pairing would be Koulibaly and Bailly at the back, as the strength that the pair possess would be no match for any strikers in the Premier League.
However, what could throw this potential transfer into major doubt is Koulibaly's exorbitant price tag of around £90m. The transfer window might be inflated these days, but to splash out almost £100m on a single player carries a lot of risks, which is perhaps why no other top side has made a bid for him yet.