The Red Devils have seen Phil Jones and Chris Smalling struggle in recent weeks, and manager Jose Mourinho is understood to be pushing for a major defensive addition this summer, with Maguire now thought to be a target.
The 24-year-old has starred for Leicester since his £17million summer move from Hull City, and having established himself as an England international, could well feature at the World Cup this summer.
Whilst thought of being big and unfashionable, Maguire has continued to impress with his ability to bring the ball out from the back, and his improving all-round game means huge clubs like United are now starting to take notice ahead of the summer transfer window.
Will Spurs regret backing away?
Leicester managed to pull off a deal for Maguire last summer, and The Sun claimed that Tottenham Hotspur were keen to land him, but backed away when they weren't prepared to match the lucrative deal offered by Leicester.
Tottenham moved on to land Ajax defender Davinson Sanchez, often using him in a back three alongside Toby Alderweireld and Jan Vertonghen, and the Colombian looks set to be a major star over the coming years.
However, seeing Maguire's value soar this season may bring a small dose of regret for Spurs, who were allegedly right in the mix to land the defender for a fraction of the fee paid to land Sanchez.
Adding another talented young Englishman may have been appealing too, and whilst Sanchez has been a great addition, Daniel Levy would surely have loved to see Tottenham be the team to oversee Maguire's value treble.