Manchester United have reportedly been told that it will take a world-record bid of more than £90m to sign Kalidou Koulibaly from Napoli in January.

United are in the market for a new central defender after missing out on a number of targets during the summer, and Koulibaly is understood to be at the top of Jose Mourinho's wishlist.

However, Napoli are reluctant to lose the 27-year-old, particularly midway through the season, and The Times reports that United will have to pay a premium price to prise him away from the Stadio San Paolo.

Koulibaly is contracted to Napoli until 2023 having signed a new deal during the summer, meaning that United would need to break the record transfer fee for a defender in order to secure his services.

Mourinho is concerned that the board will not sanction such an expensive purchase, though, with Ed Woodward thought to favour bringing in young players and then developing them.

Koulibaly joined Napoli in 2014 and is closing in on 200 first-team appearances for the club.