Manchester City’s £54million capture of Walker from Tottenham Hotspur in July 2017 was the most expensive deal ever for a defender at the time and Manchester United believe it has now distorted the market, the Manchester Evening News claim.
Ever since the deal to sign the England international was completed, transfer fees for defenders have risen astronomically.
City signed fellow full-back Benjamin Mendy the same month for a reported £52m and Ameyric Lapote in January 2018 for £57m.
The knock-on effect this has had to other clubs has been clear to see as well, with Liverpool forking out a mammoth £75m for Virgil Van Dijk and Bayern Munich splurging £70m on Lucas Hernandez.
This is now set to impact United’s transfer business with the Red Devils desperate to strengthen their defence this summer.

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Marcos Rojo, Phil Jones, Chris Smalling and Ashley Young have all inked new deals with the club in the past year but all four players were part of United’s worst defence since the 1978-79 season.
Therefore, it is no wonder that manager Ole Gunnar Solskjaer is prioritising defensive recruits as the club look to bounce back from a disappointing season.
Solskjaer took over halfway through the season but was unable to secure United Champions League football, with the club tapering off towards the end of the campaign and finishing sixth.
The likes of Crystal Palace right-back Aaron Wan-Bissaka, Ajax captain Matthijs De Ligt, West Ham’s Issa Diop and Napoli centre-half Kalidou Koulibaly have all been heavily linked with moves to Old Trafford so far this window.
However, the after-effects of Walker’s move to City look to be slowing down United’s transfer business.
They are set to go back to Palace with a third bid for Wan-Bissaka after the Eagles demanded around £60m for the 21-year-old and West Ham are also playing hardball over Diop.
The Hammers rejected an initial bid of £40m and supposedly value the Frenchman at £75m – the same fee Liverpool paid for Van Dijk.