Harry Maguire and Raphael Varane seemed like a centre-back partnership worthy of challenging for the Premier League title in the summer. United have been calamitous in defence instead and that statement looks foolish with the benefit of hindsight.
Maguire has endured a nightmare campaign. The centre-back was exceptional at the European Championship but those performances now feel like a lifetime ago - they were just nine months ago in reality. Maguire has been ponderous, devoid of confidence and unable to arrest his decline this season. There have understandably been calls for United to sign a replacement for him.
Raphael Varane was supposed to be the final piece of the jigsaw alongside Maguire. United's £34m deal to sign Varane from Real Madrid in the summer was a genuine coup and he arrived in Manchester with a CV not many currently playing could compete with.
ALSO READ: Harry Maguire's tone deaf comment insulted Manchester United fans before Liverpool disasterclass.
Varane has looked world-class when on the pitch, but the 28-year-old has become more familiar with the injury room than the noise of Old Trafford. His injury record has been disappointing. Varane is not the solution United once thought he was.
The centre-back has missed 16 matches through injury or illness this season. He was unavailable again for United's visit to Liverpool on Tuesday night and supporters have grown increasingly frustrated with the player, just like they have with Edinson Cavani for a similar reason. Varane is not injury-prone to the extent of Cavani - not many players are - but it's slowly becoming an issue.
Ralf Rangnick started Phil Jones on Tuesday night. Jones' plight is well documented and something has gone seriously wrong when he's starting against one of the world's best teams. That's without mentioning he's played under 200 minutes this term.
Jones was thrown into hot water at Anfield and he was brought off at half-time. He could leave United in the summer and Eric Bailly, who is unhappy at the club, is also expected to seek an exit. That will leave United with Maguire, Varane and Victor Lindelof. It's no wonder that the Manchester Evening News understand the club intends to sign another centre-back this summer.
United have now reignited their interest in signing Villarreal defender Pau Torres and that's basically an admission that they've got their recruitment policy wrong. Football director John Murtough will be well aware of the work United have to do.
Lindelof, Maguire and Varane cost in excess of £140m, yet Torres has been earmarked to improve United's defence. That highlights how poor United's transfer policy has been over the last few years - not that anyone needs a reminder of that.
It is understood Torres has a release clause in his current deal, which is in the region of €60m (£50m). If Torres is to sign for United, the four centre-backs at the club - Torres, Lindelof, Maguire and Varane - would have cost around £200m, but do those options reflect central defenders capable of challenging for the Premier League title? Some would argue they don't.
However, Varane remains world-class with a clean bill of health and Torres and Maguire fighting for the other starting position should ensure United are more than sound at the back. The latter doesn't deserve to start on this season's evidence.
United signing Torres would be an admission that the centre-backs they've signed over the last few years aren't good enough. Sometimes you have to admit you were wrong to move forward.
Sign up to our United newsletter so you never miss an update from Old Trafford this season.