​Manchester United have been dealt a setback as they look to bolster their defensive options after their £91m bid for Napoli defender Kalidou Koulibaly was rejected 'immediately'. 


Jose Mourinho's side have already conceded 21 goals in the Premier League this season after just 13 games, while the manager has been particularly critical of performances from his defenders at times.


As a result, Italian media outlet ​Corriere dello Sport are reporting that the Red Devils made an approach to sign Koulibaly from ​Napoli for a fee in the region of £91m, however they were rebuffed 'immediately' by the club's president Aurelio De Laurentiis. 

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The apparent swiftness of the response means that an offer in excess of the £91m would be required to prise the 27-year-old away from the Serie A side, which would be a record fee for a defender, surpassing the £75m Liverpool paid Southampton to sign Virgil van Dijk in January 2018. 


Koulibaly, who was recently nominated for the African Footballer of the Year award, has earned a reputation as one of Europe's best centre backs in recent seasons due to his performances for the Naples-based club, with the Senegal international making 182 appearances for the club since signing from Genk in 2014. 


Mourinho's desire to sign a central defender in the summer was well documented, as Leicester City's Harry Maguire was repeatedly linked with a move to Old Trafford, although that proposed transfer failed to materialise. 

SSC Napoli v Paris Saint-Germain - UEFA Champions League Group C

It could prove to be a quiet transfer window for ​United once it officially opens at the turn of the year despite his apparent want to sign new players, with Mourinho suggesting ​it's unlikely that the club will make any new signings