Manchester United has submitted a bid of €100m (£89.2m) for Napoli centre-back, according to report in Italian media.
The Old Trafford outfit has been linked with the Senegalese international Kalidou Koulibaly, according to the report in Calciomercato.
The Napoli defender was remarkable in the World Cup for the Terranga Lions in the World Cup and he is seen as one of Europe's finest centre defenders.
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Koulibaly has been on the radar of Chelsea for the past two seasons but there deal to bring the defender could not materialize.
Manchester United is ready to break the bank to secure the services of the Senegalese as Mourinho wants to rebuild the defence.