A familiar problem is responsible for the gradual erosion of Manchester United's Premier League title challenge over the past few weeks: bad defending.
After last weekend's frustrating 1-1 draw at West Brom, manager Ole Gunnar Solskjaer lamented his side's lack of creativity, but, in reality, the visitors were once again undone by sloppiness at the back.
Granted, the attack had an off-day but they still bailed out the defence, which was breached after just two minutes of play at the Hawthorns.
Mbaye Diagne’s opener offered a timely reminder that Victor Lindelof is simply not strong enough for the English top flight. But while certain individuals are not of the requisite quality to play in a title-winning team, United also have a collective problem.
At West Brom, Solskjaer's side were once again punished for sitting too deep. They failed to push to push out quick enough, as Gary Neville highlighted on Sky Sports.
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“If they don't start doing it (pushing out quickly), they're never going to get to a point where they're winning the league,” the former United defender argued. "I think teams nowadays, you have got to be aggressive in getting out of your box.”
Being too slow to get out, especially on set-pieces, is just one of the problems that has plagued the back line all season long. It has cost United points, so you can see why a centre-back is top of the summer transfer wish-list.
Dayot Upamecano, who announced last week that he will join Bayern Munich in the summer, was under consideration for a while, but United dropped their interest in him last year, after never making a serious move for the Frenchman.
However, United are interested in Upamecano's RB Leipzig team-mate Ibrahima Konate, as well as Sevilla's Jules Kounde and David Carmo of Braga.
For now, though, Eric Bailly should be starting alongside Harry Maguire in the heart of the defence, as he underlined with another solid performance in Thursday night's Europa League demolition of Real Sociedad.
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Not only is Bailly stronger than Lindelof, he's also quicker, making him a significant upgrade on the Swede.
For Solskjaer’s quick, counter-attacking football to be successful, the foundations at the back need to be firm, which is why the manager was so enthused by what he saw from Bailly & Co. in Turin.
"On a night like this, when we find spaces, we can be a dangerous team," the Norwegian told BT Sport after the game. "We had to defend well, they have some terrific players up front, and we earned the right to counter-attack quickly. They opened up and we got the spaces we wanted."
Obviously, what they want this summer, then, is a dominant centre-half who will bring even more solidity and reliability to the backline. For all his talents, Bailly has, unfortunately, yet to prove himself capable of remaining fit for very long.
Ideally, Solskjaer is looking for United's answer to Manchester City ace Ruben Dias, a top-level but not outrageously expensive centre-half capable of making a Virgil van Dijk-like impact on a defence.
Specifically, they are searching for a left-footer who is capable of winning the ball further up the pitch to spark counterattacks. United also want a player who will complement and help Maguire in a way that Lindelof does not.
For example, when the captain gets caught out for pace with balls in behind, he needs to know that his partner will be there to cover for him.
Of course, if he stays fit, Bailly can certainly do that for the remainder of the season. After a nervy start, he rediscovered something approaching his best form against Sociedad. He ended the game having made eight clearances, won 100 per cent of his aerial duels and with a pass completion rate of 85%.
Bailly may not be in the 'world-class' bracket and his fitness will always be a cause for concern, meaning he is by no means a long-term solution.
However, he is undoubtedly a better option at the back right now than Lindelof.