Talk to Arsène Wenger or Arrigo Sacchi and they'll tell you that it was the Ajax of the early 70s that shaped their philosophy. The basic tenets are simple: pass and move when in possession, squeeze the play when out of it. As Sacchi's Milan cut through Italian preconceptions in the late 80s, and Italy were beaten by Valeriy Lobanovskyi's USSR in the semi-final of Euro 88, Marcello Lippi acknowledged that "everybody plays a pressing game now".
That has long been true at Barcelona, to where Rinus Michels and Johan Cruyff exported their philosophy 40 years ago. The Ajax theory has underpinned their thinking ever since, through the Dream Team days of Cruyff in the early 90s to the present side of Pep Guardiola who, of course, played for Cruyff. In the past two decades, though, that style of play pioneered by Viktor Maslov with Dynamo Kyiv and by Michels at Ajax in the mid-60s had become, at the highest level, a universal default, at least for proactive teams.
Even those, such as the British long-ball theorist Charles Reep, who favoured a more direct approach, began to press, recognising the value of winning the ball back high up the pitch. Essentially the difference between the Reepian and Maslovian models was in what was done with the ball when it was won. Reep wanted the ball played forward quickly, believing each additional pass was the potential source of error. Maslov and Michels trusted the technique of their sides and looked to treasure the ball. After all, when you're in possession it takes spectacular bad luck or incompetence to let the opposition score.
It is possible, of course, to be successful with a reactive side, as José Mourinho was with Internazionale last season, for instance. Sit deep, absorb pressure and strike on the counterattack. The sense, though, is that the truly great sides, the 10 or a dozen who live not only in the record books but in the folk memory of the game, must be proactive.
Which is not to say they may not be defensive. There is a tendency in England to believe that defending means retreating to the edge of the penalty area and digging in for a protracted siege, but there are few better ways of defending than holding the ball in the opposition half. Look at Ajax's three successive European Cup wins: in the latter two, in 1972 and 1973, they took early leads and essentially passed the game into submission. At the World Cup, as every team bar Chile bunkered down against Spain, they opted for a policy of control, knowing that at some point the goal would come. And Barça can do that as well; often they are so superior to their opponents that they can attack almost without fear, but in big games – as in the Champions League final two years ago – they have proved themselves more than capable of protecting a lead by protecting the ball – the "sterile domination" of which Wenger spoke.
Manchester United were made to look very ordinary in that final in Rome, yet the truth is that until Samuel Eto'o put Barça ahead after 10 minutes, they were the better side. Once Barça had the lead, they simply kept the ball. The bad news for United is that the stats suggest they're getting better and better at doing so. In 2006-07, according to Opta, Barcelona had on average 61.1% possession in Champions League games. Since then that has gone up each year: to 63.2 then to 65.6 then 70.6 and this season 73.3. United will have to get used to spending long periods without the ball and will know there is an even greater imperative than normal not to concede the opening goal.
The suggestion, in fact, is that Barça have grown a little more cautious than they were two years ago, scoring 2.25 goals per game as opposed to 2.46, and conceding 0.67 per game as opposed to 1.00. It may be that you can't prioritise both position and possession, and Barça have opted to control the latter, the result being that they end up playing a little deeper. Their control of games is greater than it was, but their goal threat is lessened. Their pass completion rate is staggering: 89% at home and 90% away. United manage 82% at home and 80.2% away.
That is partly related to United's style of play. They do play the occasional longer pass partly because, having the ball less than Barcelona, they counter-attack more frequently. Similarly, United are more effective when crossing the ball – their cross completion rate is 21.7% as opposed to 17.4%. Given Gerard Piqué's occasional disquiet under aerial balls – which may have been why Sir Alex Ferguson sold him in the first place – and the possibility that Javier Mascherano will play in central defence if Carles Puyol has to cover at left-back, it is safe to assume that crosses, whether from open play or dead balls, will be one of United's two major modes of attack.
The other will be the counter-attack. United have always been adept on the break, but they are unlikely to have played many games in which they have had to rely upon it so completely. Barca hog the ball like nobody before them. How best, then, to combat them?
The best way – from a theoretical point of view anyway – may be something so radical as to be unthinkable. Given Lionel Messi plays as a false nine, dropping deep from his centre-forward's position, there is an argument to be made that a side requires only one central defender – no markers and a spare man, effectively – and that Messi is best tracked by a defensive midfielder, with the full-backs slightly tucked in to deal with the incursions from wide of Pedro and David Villa. That suggests a 3-3-3-1 shape, although not the three centre-backs, wing-back plus a holder, played by Marcelo Bielsa's Chile in the World Cup, but something more like an hour-glass: wide three, narrow three, wide three, centre-forward.
Ferguson is a tinkerer, and often comes up with something unexpected for major games, but the chances of him using an untried formation and breaking up the Rio Ferdinand-Nemanja Vidic partnership are nil. So taking the 3-3-3-1 paradigm and pushing the Messi-tracking defensive midfielder to centre-back, we're left with a 4-2-3-1, which is the shape all three sides to have beaten Barcelona in league or Champions League this season – Hercules, Arsenal and Real Sociedad – have used. That said, 27 teams have lined up in a 4-2-3-1 against Barça this season, and while three have won, 20 have lost. (The worst formation to use, statistically, is straight 4-4-2, which has a seven defeats out of seven record). What United must do at all costs is protect that space in front of the two centre-backs; Xabi Alonso did not have the best game for Real Madrid in the first leg of the semi-final, but it was after he had been forced by Pepe's red card to abandon his position just in front of the back four that Messi, granted a couple of yards of acceleration room, produced the second goal that effectively settled the tie.
United may draw hope, even, from the performance of Shakhtar Donetsk against Barça. Luiz Adriano wasted three presentable chances with the score at either 0-0 or 1-0 in the Camp Nou, before Shakhtar's defensive inadequacies were exploited. And that's part of Barça's strength; Espanyol, also playing a 4-2-3-1, really troubled them in the league game at Nou Sarria this season, pressing high, effectively taking them on at their own game, and they ended up losing 5-1. When that is the prospect for those who challenge them, it's little wonder many sides prefer simply to retreat and accept a two- or three-goal beating. The ferocity and effectiveness of United's pressing in the early stages of the recent league game against Chelsea suggest United intend to try to drive Barça back.
It will come as little surprise that the player in the Champions League to have averaged the most passes per game is Xavi with 106.9 (Michael Carrick is United's best with 74.4 – the ninth most in the Champions League this season). He is also the player to have had the most touches – 121.27 per game (United don't have a player in the top 10) – and to have received the most passes – 98.27 (again, there is no United player in the top 10). Trying to stop him settling is an obvious priority – and may persuade Ferguson to use Darren Fletcher rather than Ryan Giggs in one of the central midfield positions.
What is perhaps a little more intriguing is that second in those three categories is Sergio Busquets. Claude Makélélé's influence at Stamford Bridge began to wane after Kevin Keegan, while Manchester City manager, showed that Chelsea could be disrupted by sitting a player – in his case Antoine Sibierski – on the midfield holder. His role was ostensibly defensive, but he was also a metronome setting the tempo for everything Chelsea did. Busquets is similar, the conduit through whom almost every Barcelona move must pass; he is vital to their rhythm, something demonstrated by how much less fluent Barça have appeared when Mascherano has been used at the back of midfield.
That means Wayne Rooney has a vital role from a defensive as well as an attacking point of view, and also is a strong argument in favour of the 4-4-1-1-cum-4-2-3-1 shape United used in both quarter-finals against Chelsea. The alternative is a 4-3-3 with Rooney as a lone central striker, but that would mean breaking up his blossoming partnership with Javier Hernández, and would deny United the Mexican's pace, which could be of supreme value if they end up playing a counterattacking game. The danger is that Rooney snapping around Busquets sounds like a red card waiting to happen, but it's hard to see any other way of disrupting the metronome.
One of the outstanding memories of Sevilla's Uefa Cup final victory over Espanyol in 2007 was of the recklessness of Dani Alves's sorties, which left Christian Poulsen, nominally the holding midfielder, operating as an auxiliary right-back. That meant there was either space high on the left flank or in front of the two centre-backs, and it was from those areas that both Espanyol's goals resulted. Barça's way of dealing with the surges of Alves, who astonishingly lies fourth in the table of most touches in the opponent's half per game, is more effective, with Busquets dropping in to become effectively a third centre-back, and one of the centre-backs edging wide.
Logic suggests that the space behind Alves should be exploitable, but no side has managed that. It would be fascinating to see Ferguson leave Nani high up the pitch on that flank and try to hit him early, but more realistically Park Ji-Sung, perhaps the best defensive forward in the game will be deployed to track and perhaps check him. United's attacking chance comes on the other flank, where Antonio Valencia, who has returned from his broken leg with enhanced strength and stamina, can both drop off to help out in midfield, and run at whoever plays at left-back. Eric Abidal, Adriano and Maxwell are returning from illness or injury, so it may be that Puyol operates there. His performance at right-back in the 2009 final was clear enough evidence that he is not as clumsy as some would suggest, but neither is he a natural full-back.
For the most part, though, United are likely to be on the back foot. The cavalier style of tradition and stereotype was abandoned long ago but, even so, for United Saturday is likely to be a game of unusual containment.