When Fabio Capello attended the World Cup fixtures meeting in Zagreb at the start of the year, top on his list of priorities was to play both matches against Croatia in September. His belief was that this was the stage in the season when English players were fittest, healthiest and least likely to be sidelined by injury. Ah, well.

As he returned to the Croatian capital yesterday minus Steven Gerrard, Owen Hargreaves, Michael Owen (if Capello cares) and with Rio Ferdinand's backache a source of alarm, he may have reflected on the numbers game that has been the undoing of many of his predecessors.

Graham Taylor was without Alan Shearer for all but three matches in his doomed qualifying campaign for the 1994 World Cup and Sven-Göran Eriksson was missing Gary Neville, Gerrard and had David Beckham greatly reduced at the finals in 2002. England went to the World Cup in 2006 without a fit credible striker and Steve McClaren's biggest games for England, in Croatia and Russia, were masterpieces of medical mishap, losing key players at the airport and in training the night before the match. The last time England played in Zagreb, Scott Parker was required to make his only international appearance since March 31, 2004, and in the starting line-up, too.

In defeat, though, nobody gives much credence to these hard-luck stories, certainly not from a manager whose salary represents little more than an FA insurance policy to guard against hearing them. There is little point in Capello bemoaning the absence of at least two certain starters, Gerrard and Hargreaves, when his £6 million annual fee is supposed to represent his ability to overcome. So, no excuses, this is the test; the match that will define his first campaign as England manager, as many have called it, although perhaps not for the most obvious reason.

England's match in Croatia this evening is about the result and more, because the result will decide whether the whole concept of Capello as England manager flies or not, most particularly with his players. He has spent nine months judging them and now they will judge him: on the coherence and effectiveness of his strategies, on the worth of his preparation and on, basically, whether this damn thing works.

As McClaren discovered too late, it is not important whether the players like a manager, but whether they have faith in him. After defeat in Zagreb in October 2006, England never had total confidence when it came to the biggest matches and, against Russia in Moscow and in the deciding game against Croatia at Wembley, it showed. The same applied to Avram Grant at Chelsea. From the start, the players were suspicious of his appointment, in a way they were not when Luiz Felipe Scolari's name was announced. The CV takes a manager only so far, though. Beyond that, he has to show that he can lead his players into battle successfully, at which point they will follow him anywhere.

Walter Lippmann, the influential American writer, political commentator and the man who coined the phrase Cold War, wrote: “The final test of a leader is that he leaves behind him in other men the conviction and the will to carry on.” This is why the best managers, such as Sir Alex Ferguson, so often help to create talented apprentices (Steve Bruce, Roy Keane, Paul Ince and Mark Hughes in the Barclays Premier League alone).

Influence is achieved by only one thing: results. If Capello is to take the players with him on his mission to reform English football, he must first convince them that his ideas, which are often unfamiliar and not always well received privately, will achieve the best return. Footballers are simple creatures. They like to win, and they like to be popular. Capello's regime may be austere, but if it gets a point in Croatia or, better still, inflicts the first home defeat the nation has suffered in a competitive match, he will be looking at a dressing-room of converts. Lose, and he remains McClaren without the light touch. This is a defining game because it will shape how the players feel about him.

Kevin Keegan tried to make the England camp a jolly place to be, but results were unconvincing. Eriksson struck an appealing blend with largely efficient qualifying campaigns married to a regime that reflected a personally liberal outlook (Jamie Carragher's book contains the delicious revelation that when certain England players were discovered to be entertaining young ladies at the team hotel, instead of reading the Riot Act, Eriksson patiently explained that this was unnecessary because if a player saw a woman he liked, he should simply get her telephone number and arrange to meet at her house after the match).

Capello does not share his indulgence. He does not even let them have a go at the Dolly Mixtures, let alone the dolly birds, to judge from the rumours about his dietary regime, and if players are publicly talking up his methods at the moment, that is because players always do. On Monday in Barcelona, Joe Cole said that he was desperate for an England manager to give him a long run of games in which he did not feel he was on trial, and in the next breath praised Capello's wisdom in making established players fight for their places. The two concepts are, plainly, mutually exclusive.

Cole was putting a positive shine on Capello's management, the way players do, because only a fool criticises the man dispensing caps for England. Beckham never said a bad word about McClaren in public, even when he dropped him.

What is said in private, however, is a different matter and, in defeat, tends to differ vastly from the official press conference line that it was the fault of the team, not the coach, and everybody is behind the boss 100 per cent. I am yet to hear an England player opine that the finest footballers in the country should have been able to pull off three at the back in Zagreb two seasons ago, but have heard plenty moan about how little time there was to prepare for the change. If the lights on Capello's Christmas tree go out this evening, whatever the brave face in public, questions will be asked in private.

Footballers are no different to the rest of us. If you are barely able to function at your job because you are snowed under with work, who do you blame? The boss. Football is the same. If your midfield is overrun, the manager should have seen that coming. If the guy on the left is not up to the task, why the hell was he promoted? In victory, it all falls into place. No player clutching a winner's medal doubts the guy who picked him. If Capello can revive England from the low of failing to qualify for the European Championship, he may spawn a generation of young English managers who believe in running their team like a US Marine boot camp. Hey, stop whining, son. I played under Fabio and it worked for me.

A case in point: José Mourinho at Chelsea. When the club were dominating the top flight, I talked to John Terry about the manager's methods. He said that everything was prepared in a three-week period, pre-season. Mourinho would go through game plans, the favoured 4-3-3 system, set-pieces, positioning; he would produce a blueprint for the entire campaign. He would tell the players to study it, because there would be no time allotted for revision once the fixtures began and any player not up to speed on the Chelsea way would not be in the team. Frankly, it all sounded barmy.

Maybe there was more room for improvisation than Terry suggested, or perhaps Mourinho was genuinely so brilliant that he had addenda covering every eventuality, with titles such as “What to do if we go 2-0 down away to Bolton Wanderers on a wet Tuesday”. Either way, his captain had bought into it entirely, because Mourinho had made Chelsea league champions. Had his first two years ended in failure, such a unique method would no doubt have been dismissed as an incomprehensible gimmick.

Keane, the Sunderland manager, recently stated that Brian Clough was the greatest manager he had worked with, yet in his autobiography he remembers being punched in the face by him as a young player for the crime of passing the ball back to the goalkeeper. Clough is dead, Keane is two decades older and the incident is no doubt now a colourful anecdote rather than a source of outrage. But the main reason Keane forgives his mentor is because Clough made him one of the greatest midfield players of the modern era. And if it took the odd right cross to do it, well, that was probably for the best.

As it stands, Capello's style remains unproven with English players at international level. The results and performances in friendly games have been unconvincing and nobody is going to get too carried away about a 2-0 win against Andorra. Meanwhile, there have been grumblings over meal times and the long afternoons the players spend confined to their rooms. Some question the wisdom of Capello's constant turnover of personnel in training routines, too, which has left individuals unsure of whether they are in the team and, if so, who will be playing beside them.

And faith, or otherwise, in all of this will flip on something as variable as a goalkeeping error or the divots on the pitch at the Maksimir Stadium. That is what did for McClaren the last time. Paul Robinson strayed off his line and was lobbed by a soft header; Neville's back-pass skipped unexpectedly to add the sprinkling of humiliation. The manager was never the same again. He came in looking to introduce new ideas and tactics but, after that, retreated to the familiar.

Capello's big ideas are more variations on a theme, but they still need the belief of his players to make them work. “The music is nothing if the audience is deaf,” Lippmann wrote. A defining game, indeed.