The back three has slowly crept back into fashion over the last few years.
A decade or so ago, the three-man backline had almost become obsolete due to the proliferation of single-striker systems.
Traditionally, a back three would operate with two of the trio tasked with marking the opponents’ centre-forwards, and one available to drop slightly deeper as additional cover, while also often being the free man to take possession and bring the ball out of the back.
When most teams adopted 4-3-3 of 4-2-3-1 shapes, with just a single dedicated striker, those utilising a three-man defence found that having two spare men at the back was overkill, and led to them being outnumbered in other areas.
But, recently, the back three has become en vogue. When Antonio Conte became Juventus manager in 2011, he started out using a 4-2-4 system in Turin, but quickly learned that his side’s strength lay in their central defenders, and elected to play three of them at once in a 3-5-2 formation.
He subsequently led the Bianconeri to three successive Serie A titles. When Massimiliano Allegri replaced the now-Chelsea manager in 2014, he had some success with a 4-3-1-2 shape, retaining lo scudetto and reaching the Champions League final. But the former AC Milan coach has since reverted to 3-5-2 to once again get the best put of the ‘BBC’ back-line of Leonardo Bonucci, Andrea Barzagli and Giorgio Chiellini.
When at the helm of the Italian national team, Conte implemented a 3-4-3 system ahead of Euro 2016, and has recenty done the same at Chelsea.
In his final season at Barcelona, Pep Guardiola adopted a 3-4-3. The reason was two-fold: firstly, he felt that his side had grown somewhat complacent and saw the switch away from 4-3-3 as a way to reinvigorate his line-up; secondly, it enabled him to get Cesc Fabregas into the same midfield as Blaugrana legends Andrés Iniesta and Xavi.
At Manchester City, Guardiola has again switched to a back three in recent weeks. This time out of an apparent mistrust of his full-backs.
The last time we saw a three-man back-line at Old Trafford was during Louis van Gaal’s first campaign with Manchester United.
The veteran Dutch coach had just used a 3-5-2 set-up to guide the Netherlands to the semi-final of the 2014 World Cup.
Upon arriving in Manchester, van Gaal saw that his central defensive options were extremely limited. And, seemingly not trusting the Red Devils defenders to provide adequate cover in a back four, opted to recycle his Oranje formation as a way of providing extra rear-guard insurance; three bad centre-backs should be stronger than two bad centre-backs, right?
United’s personnel were unsuited to 3-5-2, though. Shouts of "4-4-2, 4-4-2," could be heard from the terraces as fans implored the manager to switch to a more familiar formation.
After stumbling through half of the season picking up below-par results, van Gaal abandoned the back three in favour of 4-3-3; the Red Devils’ fortunes almost immediately improved.
So, the 3-5-2 experiment was a bust for United. But, with a different set of players, could it be worth revisiting?
As it stands, with Eric Bailly likely to be out for a couple of months, José Mourinho simply doesn’t have the numbers to make it work.
But once the 22-year-old Ivorian returns there could be some merit in trying 3-5-2 again, or even 3-4-3.
At the back, it would allow Chris Smalling, who has been caught out defensively of late, to concentrate on just one aspect of the job: either marking or dropping off to cover, rather than having to worry about how, when and where to do a mixture of each.
Alongside him, Daley Blind could be the spare man tasked with bringing the ball out from the back and utilising his superb range of passing to instigate attacks. And Bailly, with his recovery pace and accurate distribution, could do an amalgamation of the two roles to varying degrees depending on the opposition.
Both Luke Shaw and Antonio Valencia appear tailor made for the wing-back roles on either flank.
Shaw would be buoyed by the slightly reduced defensive responsibility and would be afforded greater freedom to push forward and provide width. While Valencia, a winger by trade, could do the same on the right, still cognisant of the defensive tasks he has performed so well this season.
Perhaps the key gain in switching to a 3-5-2 would be in central midfield, where £89 million record signing Paul Pogba could resume the exact role in which he thrived with Juventus: left of the midfield three. In this instance, Michael Carrick or Morgan Schneiderlin could play the Andrea Pirlo role of deep-lying playmaker, while Ander Herrera would be Arturo Vidal, providing energy and drive in a box-to-box role on the right.
In attack, Zlatan Ibrahimovic, who has looked isolated and immobile too often this season, would get a partner. Either Anthony Martial or Marcus Rashford could be the speedy foil to Zlatan’s creative instincts.
Or, if 3-4-3 is the preferred option, just as Diego Costa has found for Chelsea of late, Ibrahimovic would be better supported by two wide players acting as inside forwards. At Chelsea, it’s Eden Hazard and either Willian or Pedro; for United it could be any combination of Rashford, Martial, Henrikh Mkhitaryan, Jesse Lingard and Juan Mata.
With the wing-backs providing the width, the wide attacking players are able to shift inside and get closer to the central striker.
The back-three idea was an unqualified failure for United two years ago, but that doesn’t mean that the same would be true this season.
Now, Mourinho has never set up any of his previous sides with a three-man defence. Since the 4-1-2-1-2 of his Porto days, the Portuguese coach has been married to either 4-3-3 (first Chelsea spell, Internazionale and plan B at Real Madrid), or 4-2-3-1 (Madrid, second Chelsea spell and United this season). So we are unlikely to see such a radical change.
Food for thought, at least.