The Senegal international has spent nearly six seasons with Napoli and he has been a consistent performer at the heart of the defence, where he has made 233 appearances.
The Serie A outfit have been reluctant to sanction his departure in recent seasons but their stance has changed with the genuine possibility that they will miss out on the Champions League next term.
In such a case, the club’s hierarchy are likely to seek to lower their wage bill and Koulibaly is apparently one of the high-profile players, who could be sold at the end of the season.
According to Le Parisien, Paris Saint-Germain and United have been keeping a close eye on Koulibaly’s situation but the former may not afford to sign him in the next transfer window.
The club are eyeing a replacement for veteran star Thiago Silva but it is suggested that Koulibaly, who is valued between £44m and £62m, is financially out of their reach.
While the capital outfit are likely to spend, the priority appears on the permanent signing of Mauro Icardi for around £61m while they need to bolster their full-back positions.
Both Thomas Meunier and Layvin Kurzawa are entering the final weeks of their contracts with the club and they have been fancied to leave as free-agents.
As a result, United are said to hold the clear advantage in the pursuit of Koulibaly and it remains to be seen whether the club will make a formal approach to sign him.
United currently have Harry Maguire and Victor Lindelof as the regular central defensive partnership but Ole Gunnar Solskjaer is said to have concerns over the latter’s displays.
Koulibaly will turn 29 next month but he continues to provide a dominating presence in the defence with his strong ball-playing and tackling abilities.
It now appears that he could be available for as little as £44m and that could tempt them to make a renewed attempt to sign him during the summer.
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