Former manager Jose Mourinho had previously insisted the position had to be improved upon, only to clash with the hierarchy over the signings he wanted due to their age and price, The Independent reported.
Napoli's Kalidou Koulibaly has long been a desired target, but sources say the current asking price of over £90 million is far too much.
That could well see United return to previous options like Leicester City's Harry Maguire and Internazionale's Milan Skriniar.
There is some debate about Toby Alderweireld's suitability, given his age, at 30.
United would prefer to go for younger players, who can slot into the team right away, but also have scope to improve.
It is meanwhile expected that Axel Tuanzebe will be recalled from his loan at Aston Villa for next season, after impressing there during the Championship club's run to the play-offs.