In contrast to the midfield options, the market for full-backs is more complicated, while some of the best Premier League players in the position over the last few years did not learn their trade patrolling the flanks.
Just look at Arsenal, who have converted Ben White, Riccardo Calafiori and Jurrien Timber to the position from centre-back with great success. Or take Pep Guardiola turning Josko Gvardiol from centre-back to left-back and then back to centre-back, or calling Matheus Nunes "one of the best midfielders in the world" when he played for Sporting CP before concluding that he "wasn't intelligent enough" to play in the middle of the park and was much better suited to playing at right-back. Guardiola has also used Nico O'Reilly in a variety of roles, with the England international switching between left-back, holding midfield and attacking midfield.
If United want a traditional overlapping, marauding left-back then they should look to Newcastle's Lewis Hall. His team-mate Tino Livramento, who is being targeted by City, is also a tempting option at right-back, but his injury history should ring alarm bells. The stumbling block for both players is their transfer fees, with Newcastle likely to charge in the region of £80m for either player.
If United want a player who has already proven themselves in the Premier League - and the success stories of last summer contrasting with the struggles faced by the likes of Manuel Ugarte, Joshua Zirkzee and Rasmus Hojlund in previous years suggest they should - then they could find value in the market by looking to Pedro Porro in the event that Tottenham get relegated, or Ola Aina if Nottingham Forest go down.
Hugo Bueno, almost certain to be relegated with Wolves, is an even lower cost option given he would be available for potentially £20m despite having some of the most impressive underlying stats in the Premier League.