Manchester United's defensive concerns are no secret.
Despite the club's recent forward strides, United's back line is, and will continue to be, an achilles heel in Ole Gunnar Solskjaer's team until it is addressed. Bringing in a top quality centre-half soon is totally necessary, but the question around when they'll address it remains.
Most fans believe they'll need to do it in January if they want to mount any sort of challenge to Liverpool's Premier League crown this season, but a summer purchase looks the more realistic option.
But making the best of what they've got is also a source of debate. Solskjaer fielded 11 different sets of central defenders during the year 2020 (including back threes) and supporters still disagree on how the Norwegian should best set up his rearguard.
So, what is the best combination for United? And should the club bring in reinforcements, which pairing is the one you build on to shore up the defence?
6. Phil Jones & Harry Maguire
Jones and Maguire were Ole's favoured centre-back partnership against Burnley in a 2-0 defeat in January.
The fact that the two have never been picked as a duo since says it all. Despite their physical nature, the two were outfought by Burnley on the night. The two seem like a disaster waiting to happen.
5. Victor Lindelof & Phil Jones
Phil Jones is the common denominator in United's poorer centre-back pairings. Despite Sir Alex Ferguson famously suggesting that Jones could be one of the all-time greats to wear the shirt, injuries have led to a stagnation.
When the two have played together there is a composure in their play. However, defensively you wouldn't back them against the very best attackers that you find at the top level.
Jones finds himself very much on the outside looking in at Old Trafford, so you would expect United to cut their losses and move him on in the near future.
4. Harry Maguire & Axel Tuanzebe
Maguire and Tuanzebe is a pairing that on paper shows great promise, although it's a combination that is seldom called upon.
The latter's injury problems have made it almost impossible for the 23-year-old to really establish himself in the first team. However, as his strengths lie in his intelligence, pace and indeed physical presence, it won't be long until he finds himself playing regularly at centre-half for United.
As a pairing, the two have a lot to learn, as seen in United's embarrassing loss in Istanbul, where Tuanzebe was hauled off at the break. There is no doubting though, that if this pair can be allowed a run of games they will grow into a strong duo.
3. Victor Lindelof & Eric Bailly
Victor Lindelof and Eric Bailly is a centre-back pairing that was tried, tested and failed during Jose Mourinho's tenure. Their unconvincing performances were the reason United had to look elsewhere and sign Harry Maguire for £80m, which just signals the club's desperation at the time.
More recently, though, the two featured together twice in a flat back four. In both cup games, the pair kept clean sheets and United managed 3-0 victories away from home against Derby County and Brighton respectively.
The two deserve great plaudits, because a week prior to the League Cup victory against the Seagulls United had scraped a 3-2 victory in the league where Brighton were unlucky to go away empty-handed after missing a whole host of opportunities.
The two were dominant when together and complimented each other well, which suggests the two have both matured since the Mourinho days. The fact that they are seldom fielded as a pair, with Harry Maguire ever-present in the league, is the reason why they are not ranked higher.
2. Victor Lindelof & Harry Maguire
Victor Lindelof and Harry Maguire is United's most common partnership at centre-back. Whether it's injury concerns with other defenders or just great trust in the two, Solskjaer is more likely to pick them than any other combination.
Both players were in the top four players in Europe for minutes played in 2020, with the United captain topping the list and Lindelof coming in at fourth. That stat alone shows how important they are for club and country.
Individually, there are some traits that mean they are extremely important to United, namely Lindelof's reading of the game and composure along with Maguire's aerial ability. The two also have an outstanding passing range.
As a partnership though, the two are just too inconsistent and that inconsistency and vulnerability sets the foundation for a shaky team, meaning going forward the two may not be the best centre-back combination as United's ambitions grow.
1. Harry Maguire & Eric Bailly
For Solskjaer, Bailly and Maguire is a partnership that has now emerged as perhaps United's most effective. At the beginning of the year, the duo could be seen playing in the cup games against the likes of Club Brugge and Norwich.
In recent weeks, Bailly has come in at centre-back and has proved to be that missing link that United needed to shore up the defence. Unlike Lindelof and Maguire, Bailly complements the United skipper better with his recovery speed. Bailly's pace allows United to play with more of freedom going forward, not afraid of the ball over the top.
Against Everton, Leicester and Wolves in recent weeks we've seen that United can focus on creating goals rather than preventing them. The two seem to have a greater understanding, which is why they are United's standout pairing.
Saying this, however, they are still the combination that did let six in against Spurs at the start of the season, suggesting the pair are by no means a Rio Ferdinand and Nemanja Vidic partnership, which begs the question: will United rest on their laurels or use their recent form as an opportunity to build on their defence? We'll be getting an answer soon enough as the transfer window creaks open.