The Italy international only joined I Rossoneri from fellow Serie A giants Juventus in July 2017, but has struggled at the San Siro, with his side certain to finish outside the league’s top five for the fifth consecutive season.
United boss Jose Mourinho is thought to have made Bonucci his top priority ahead of the transfer window as he looks to strengthen his squad in order to close the gap to Premier League champions and local rivals Manchester City.
The Red Devils may have finished as the best of the rest in England’s top flight, but in the final standings they were 19 points behind Pep Guardiola’s rampant Citizens.
Victor Lindelof has looked shaky since his arrival from Benfica and Mourinho clearly wants to freshen a defence that was the second tightest in the division with just 28 conceded.
Although Phil Jones and Chris Smalling enjoyed fairly solid campaigns, the former is extremely prone to injury and as such cannot be trusted to play for a full term.
Eric Bailly’s second season at the club was interrupted by injury but many United fans still see him as the future at the heart of the backline.
As for Milan, they will look to recoup as much of the €42 million (£36.7 million) that they paid Juventus for Bonucci as possible, but his value has undoubtedly decreased in the intervening 10 months.
Nonetheless, the 31-year-old is the kind of experienced warrior that Mourinho likes in his teams and could prove to be a shrewd acquisition in the short term.
After beating Watford 1-0 on the last day of the Premier League season, United are now looking forward to an FA Cup final date with Chelsea on Saturday evening.