The Senegalese powerhouse has been a long-term target for Old Trafford chiefs, particularly for former manager Jose Mourinho.
Mourinho was keen to sign a centre-back last summer and Koulibaly was reportedly on the top of his wish-list.
But a move for a centre-back never materialised – a decision which the Portuguese bemoaned repeatedly before he was sacked.
However, according to La Gazzetta dello Sport, United are set to break the bank to tempt the Serie A side into selling their star defender.
Napoli president Aurelio de Laurentiis has told Red Devil deal-makers that a bid in the region of £128million will be enough to prise him away from Italy.
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However, the Red Devils are not alone in their pursuit of the defender.
Barcelona, Real Madrid and Chelsea are all monitoring the situation of the 27-year-old, who has made 143 appearances for the Gli Azzurri.
Should Man United offer Napoli their asking price, the Italian outfit will make a huge profit on their player, who signed for just £6.5million from Genk in 2014.
Furthermore, the move will smash the world record fee paid for a defender. – surpassing the £75million Liverpool paid Southampton for Virgil van Dijk last season.
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