However, despite Napoli president Aurelio De Laurentiis having only reportedly reduced the price-tag to a still hefty £85m, that figure may be enough to tempt United into an approach during the summer.
Here, Sports Mole predicts how United could line up if they are able to secure the services of the 28-year-old.
If Solskjaer finds himself with four world-class centre-halves at his disposal, it will increase the chances of the United boss using a three-man defence on a regular basis.
Traditionally, United managers have opted against such a strategy, but Solskjaer knows that he needs to be versatile in order to compete with the top teams in Europe.
Despite Maguire's recent promotion to club captain, the England international would likely switch to the left-hand side of a back three to accommodate Koulibaly, who could slot into the centre.
In most cases, that would leave Lindelof and Bailly to compete for the final position on the right, while Luke Shaw would be able to provide backup in the event of injuries or suspensions.
However, there would inevitably be occasions, especially at Old Trafford, when Solskjaer would prefer to use a back four, a scenario which would likely see Koulibaly partner Maguire.
Regardless of the tactics, a central midfield three is likely to become the norm now that Bruno Fernandes has arrived at the club, with the Portuguese able to be deployed as the link man between defence and attack or in the number 10 role.