Ole Gunnar Solskjaer is still trying to find the ideal partner for Harry Maguire in a bid to create a Premier League title-winning defence.
Victor Lindelof has been used most-consistently alongside the £80million centre back, but Solskjaer is weighing up options from within Old Trafford and outside, with questions over Manchester United’s vulnerability when faced with pace.
Their Norwegian manager is intent on playing with a high line - encouraging his defenders to take risks by playing out from the back. And while United recorded the third best defensive record in the league this season - conceding just three more than champions Liverpool - there remain doubts as to whether it is robust enough to prove the basis of a title challenge.
Solskjaer began the campaign with the intention of giving Axel Tuanzebe chance to stake a claim to partner Maguire.
The academy graduate was immediately promoted above Chris Smalling and Marcos Rojo in the pecking order - leading to both of those players being sent out on loan. But fitness issues have halted his progress when Solskjaer had hoped 22-year-old would make his mark in the manner of Mason Greenwood and Brandon Williams.
Solskjaer places great importance on physical robustness from his players - and that will be even more important next season when he expects to mount a title challenge as well as going deep in the Champions League.
Smalling’s return from a season-long loan at Roma has presented Solskjaer with a dilemma.
Should buyers be found for Phil Jones and Rojo, Smalling would be an experienced addition to the squad, even if he is not the ball-playing centre back Solskjaer prefers.
Whether the 30-year-old would be happy to be used as back-up after such an impressive campaign in Serie A is another issue.
Academy player Teden Mengi will be given more opportunities next season - but Eric Bailly is best-placed to break up the Maguire/Lindelof partnership from within.
In Pictures | Manchester United vs FC Copenhagen | 10/08/2020
Solskjaer believes there is a top-class talent in the Ivory Coast international if he can remain consistently fit.
Fast and aggressive, he could be an ideal foil for the more cultured Maguire.
His sometimes reckless lunging needs to be ironed out of his game, but Solskjaer believes there are raw materials worth persevering with.
Even still, he is considering external options.
Nathan Ake (below) was among the potential targets before his £40million move from Bournemouth to Manchester City.
Kalidou Koulibaly is a dream target, with Solskjaer a long-term admirer. But his £70million-plus price tag will be prohibitive as United focus on Jadon Sancho for a similar fee.
They are monitoring Lille’s Gabriel Magalhaes, whose £20million valuation makes him a more affordable option.
But Solskjaer will have to be sure.
He is reluctant to look too far down the list of options drawn up by United’s transfer committee, which is underlined by his determination to persist with Bailly, who was given the nod against Copenhagen on Monday.
Bailly was ultimately replaced by Lindelof, with Solskjaer concerned he could be sent off after picking up a second half yellow card.
It was another reminder of the rough edges that need to be smoothed if he is to develop into the player United hope he will.