Maguire completed his £80million move from Leicester City to Manchester United on Monday afternoon.
The 26-year-old’s transfer to Old Trafford has made him the most expensive defender in the world, a title which was previously held by Liverpool’s Virgil van Dijk.
Maguire’s fee has prompted plenty of comparisons between himself and Van Dijk, who played a key role in Liverpool’s Champions League triumph last season.
Collymore is a big fan of both defenders but believes Van Dijk has so far proven to be far better value for money than United’s newest recruit.
“Manchester United finally got their man on Monday with the £80m capture of Harry Maguire but they have paid double his true worth,” Collymore told The Mirror.
“United unveiled their big-money buy on a six-year deal from Leicester after a lengthy pursuit which started last summer after the World Cup.
“I like and respect England stopper Maguire who is a very good player, leader and influence in the dressing room.
“But the 26-year-old is not in the same class as Liverpool’s Dutch stopper Virgil van Dijk. For a British central defender with leadership qualities, Harry fits the bill.
“But if you want premium quality to push you to a title or Champions League then Van Dijk is your man.
“Maguire, even in an expensive market, is overpriced and United have played twice the price of his realistic value in my view to make him the world’s most expensive defender.”
Van Dijk has been imperious at the back for Liverpool since joining them from Southampton in December 2017.
And Collymore reckons the Netherlands international’s value to the club has skyrocketed to the point he could once again become the most expensive defender on the planet if Barcelona, Real Madrid or Paris Saint-Germain come calling.
“His price tag means he now eclipses Van Dijk, 28, who became the world’s costliest defender when he joined Liverpool from Southampton in January 2018 for £75m,” Collymore said of Maguire. “But that has proven to be worth every penny.
“I remember people talking about Van Dijk back at Celtic and saying this guy is a Rolls Royce.
“He is now looking a bargain because the Dutchman has to be worth £200m to a Barcelona, Real Madrid or PSG as he is that influential and that good. Maguire is going to have to step up and then some to prove himself as good a signing.”
Maguire is in line make to his Manchester United debut on Sunday afternoon when the Red Devils welcome Chelsea to Old Trafford for their opening fixture of the 2019/20 Premier League season.