Antonio Conte’s decision to adopt the 3-4-3 formation at Chelsea has been influential in the narrative of the Premier League season. While Manchester United, Manchester City, Arsenal, Liverpool and Tottenham Hotspur have stumbled over different formations and team selections, Conte has persisted with the shape that brought him so much success with Juventus and the Italian national team. Chelsea’s balance of defensive solidity, work ethic in midfield, and mercurial attacking talents have pushed the Londoners to within touching distance of the title.

Indeed, Conte’s tactical revolution is taking the English league by storm, with various opponents attempting to mimic Chelsea’s success. Only Spurs have fully implemented the formation to a similarly devastating effect, while Crystal Palace, Watford and City have all experimented. Palace and Watford lack the quality to succeed, while Pep Guardiola’s side is probably short of the right players for the roles envisioned.

José Mourinho has also tinkered with the 3-4-3 in recent weeks, despite being accused of losing touch with modern football. The trial has offered mixed results. Mourinho deployed a back three in the first leg of United’s Europa League Round of 16 fixture with Rostov in Russia. The fixture was played on a surface that would not look out of place in the Sunday Leagues, and the Reds struggled to create any kind of tempo.

United also shifted to a back three against Chelsea at Stamford Bridge in the FA Cup. It was billed as a litmus test for Mourinho’s newfound formation, and the contest looked even until Ander Herrera’s dismissal. Having lost a man against the league leaders, United parked the bus and played a back six for the remainder of the game.

The final outing of the system to date was in United’s Europa League home leg against Rostov. With a lower-quality opposition at Old Trafford, many observers expected Mourinho to roll out United’s full offensive capability. The visitors, however, were well organised and subdued much of United’s attacking threat until Juan Mata scored the only goal of the game 20 minutes from time.

United reverted to a more familiar system against Middlesbrough at the weekend, but the brief experiment with three at the back has offered some food for thought.

Squad depth in defensive positions

Simplistically, a back three offers more defensive options than with a regulation back four. The extra centre back allows the full-backs take up higher positions on the pitch, although the wide players still perform defensive roles for the team. This plays to United’s advantage, with the Reds enjoying squad depth at centre back.

There have been times this season when the form of Eric Bailly, Marcos Rojo, Phil Jones and Chris Smalling has offered the manager a selection headache, while Axel Tuanzebe and Timothy Fosu-Mensah are youthful options on the periphery. Bailly has enjoyed a strong début campaign, while Jones and Rojo have, at times, fashioned a strong partnership. Although Smalling’s form has fluctuated, Daley Blind illustrated during the 2014 World Cup that, despite lacking pace, he is comfortable playing in a three-back.

Mourinho also boasts good options at wing-back, with players possessing the necessary industry and pace to perform in the role. This season Spurs’ Kyle Walker and Danny Rose and Chelsea’s Victor Moses and Marcos Alonso have demonstrated the importance of wing-backs in the system. United could mirror the London clubs in that department, with Antonio Valencia and Luke Shaw potentially two of the finest in the Premier League. With Blind’s quality of delivery and Ashley Young’s relative experience as an attacking full-back, United has some strength in depth.

Variety in forward positions

Conte prefers trickery and pace in wide forward positions, with Eden Hazard and one of Pedro or Willian, supporting lone striker Diego Costa. Over at Spurs Mauricio Pochettino prefers one of his wide forwards, normally Christian Eriksen, to have creative license while the other, Dele Alli, supports Harry Kane.

United could adopt either approach. With Zlatan Ibrahimović leading the line, Mourinho is able to draw on Henrikh Mkhitaryan or Juan Mata as wide playmakers in a 3-4-3 system, with Anthony Martial and Marcus Rashford providing a second-striker’s quality on the left. This system might allow Mourinho to switch fluidly between a dynamic front three and a more rigid two striker partnership, with a supporting midfielder. It opens up the possibility of Paul Pogba using his talents closer to the opposition’s goal

Mourinho’s style

It is unfair to call the Portuguese manager a defensive coach, although Mourinho holds a natural preference for defensive solidity over attacking flair. There remains some truth in Mourinho’s assertion that he is upholding United’s attacking traditions. During United’s glory days in the late 90’s, Sir Alex Ferguson’s preferred style was based on defensive solidity and vertical passes, launching fast counter attacks, predominantly through the flying wingers.

The league leaders have adopted the 3-4-3 system for many of the same reasons, with the team able to defend deep and then look to hit the forward players quickly when possession is overturned. If the opposition is stretched, the three forwards can often mount a dangerous attack by themselves. If reinforcements are required, the overlapping full-backs can provide an overload in wide positions, particularly if the ball is switched quickly by one of Chelsea’s two central midfielders.

It’s a style of that applies to many of Mourinho’s best teams. The manager prefers taking fewer risks, while reaping the attacking rewards when executed correctly. The Portuguese focusses his coaching on the defensive aspects of football, while allowing his forward players freedom to use their own ingenuity and personality.

It was unsurprising that United’s only goal against Rostov at Old Trafford came when the Reds allowed the Russian side to retain possession. The home side seized the ball on the half way line and broke quickly against Rostov’s high line; a combination of quick passes between the front three ended when Ibrahimović teed up Mata with a smart back-heel for the Spaniard to tap home.

Yet, for the majority of the game, United held possession in Rostov’s half and created few clear-cut chances. It offered an indication that the Reds may still be suffering a hangover from the Louis van Gaal era.

Pogba may struggle in 3-4-3

If the 3-4-3 system may superficially suit Mourinho’s personnel and style, it might not fit the team’s £89 million star player. In the system two central midfielders shield three centre backs when the wing-backs have pushed up to create overloads. For example, at Spurs, Victor Wanyama and Mousa Dembélé are used to great effect in the centre of the park, with both players capable of breaking up play and launching vertical passes. Chelsea deploy N’Golo Kanté and Nemanja Matić to perform a similar task, with Cesc Fabregas occasionally filling in for the Serbian against lesser teams.

Pogba offers some defensive capabilities, but there is no doubt that the Frenchman is a far better player when given freedom to roam from box-to-box. Against Chelsea, Pogba struggled to track runners from midfield as the game wore on and his positioning was far too deep to have any effect on United’s attacking play.

Ander Herrera has enjoyed a fine season, breaking up play and performing at a high level, yet the Spaniard cannot provide adequate defensive cover if the Frenchman is allowed to roam forward. It would leave Mourinho with three options if he wanted to persist with a three-man defence in the longer run, none of which are ideal. Firstly, Pogba can be given license to roam while United reign in the wing-backs. It might have the effect of making the side narrow and predictable. Pogba could be asked to perform a more defensive role alongside Herrera, but it would waste his myriad attacking talents. Finally, Pogba could be dropped for a more defensively astute midfielder – a solution palatable to nobody.

My Opinion : a dynamic system, but probably not for United

The system has proved a master stroke for Chelsea this season, and variations of the formation are quickly being adopted by some of the most exciting clubs across the continent, including Borussia Dortmund and Barcelona. The system offers flexibility in attack and defence, providing every player is an ideal fit for their given role. Mourinho has many of the players available to switch to the system permanently; the big sticking point is his star man. It is probably a defining factor the debate.