Manchester United move into one of the greatest crises the club have known since Sir Alex Ferguson took over as manager. I am highly tempted to predict instant and total disaster. The only thing that stops me is that every time I have done this in the past, that extraordinary man has somehow turned things around. He is the greatest manager of them all at the art of turning crisis into achievement.

But this is his supreme test. How he copes will define the way we think of him. If he plays it right, his greatness will be incontrovertible and for all time; if he gets it wrong, his record must always have some kind of qualification, some kind of asterisk.

What he faces is the test of the second impostor.

Most of us only get to meet the first impostor. Kipling’s two impostors should perhaps be given a brief introduction for those of us who don’t get to play on Centre Court, those eternal lines from If: “If you can meet with Triumph and Disaster and treat those two impostors just the same . . .”

Though Triumph is listed first, it is Disaster most of us know first, the impostor most are familiar with. But the impostures of Triumph are infinitely more subtle and potentially far more damaging. Ferguson’s task over the next few weeks is one of the hardest he has faced. He must deal with the intergalactic Triumph of United’s 7-1 victory over AS Roma in the quarter-finals of the Champions League.

It was a night of stardust. Everything United did came off. It was a day when real life took a holiday. Football was easy. It was the complete triumph, fulfilment and justification of Ferguson’s work since he created this, the latest of his remarkable United teams, over the course of the past three years.

The only trouble is that this glorious climax has come a fair way before the season’s conclusion. Nothing has been won; but the team will never be quite as good again. Nothing will ever be as easy, as wonderful, as glorious. And it is dealing with this letdown that defines teams and individuals.

I was reminded, a trifle obscurely, of the glorious victory by the great Colombia side that beat Argentina 5-0 in 1993, with Carlos Valderrama, Faustino Asprilla and Adolfo “El Tren” Valencia. They were perfect — I was convinced they would win the World Cup the following year. Mind you, so was Pelé. But Colombia went home in disgrace, one of their number, Andrés Escobar, to murder.

The sporting world is full of individuals and teams who have failed to cope with the second impostor. Arsenal still live in the shadow of the Invincibles of 2003-04. The trauma of their defeat in the “Battle of the Buffet” still haunts them. Arsenal have never recovered from their season of invincibility.

We must look at the national teams to see the second impostor at his most dangerous. The England football team are still suffering from that 5-1 victory over Germany in Munich in 2001. Germany recovered from Disaster and went on to become World Cup finalists in 2002, semi-finalists four years on. But England never recovered from Triumph. They acquired the habit of blinking in the face of destiny. A single day as world-beaters had undone them. Years on, they are still unable to see themselves as a team of born battlers — and yet to see themselves as inevitable champions is equally impossible. The golden generation was blinded at its first glint of gold.

The greater the Triumph, the greater the devastation. The England cricket team have failed spectacularly to deal with the triumph of the Ashes win in 2005. They stepped on the open-topped bus as champions; they stepped off as shadows. To watch them make heavy weather of defeating Bangladesh on Wednesday was to see a side that lacked every trace of self-certainty. That tentative, poking-and-prodding batsmanship was of a side convinced of nothing save its own mediocrity.

The worst of it all was in Adelaide last autumn. The last day of the second traumatic Test match in defence of the Ashes was one of the most extraordinary bits of sport I have seen. England were beaten: from a position in which defeat was impossible.

As my old friend Matthew Engel summed up in Wisden: “England were at once worn out but underprepared; complacent yet overapprehensive; inward-looking yet dysfunctional as a unit; closeted yet distracted.” The effects of the second impostor could hardly be better described.

Meanwhile, the rugby union team is still, four years on, struggling to deal with the Triumph of the World Cup in 2003. The combination of injuries and retirement created a team without a centre, without a leader, without a sense of corporate identity — just a bunch of ordinary Joes with an impossible thing to live up to.

This combination of circumstances has broken one team after another, one individual after another. The team played well in flickers and fits and starts over the recent Six Nations Championship, but they go into the World Cup this autumn as the least certain world champions in the history of sport.

The second impostor affects individuals as well as teams. Jenson Button has never recovered from the triumph of becoming a Formula One driver at the age of 19. At the same age, Pete Sampras won his first grand-slam title, the US Open, in 1990. And it was almost too much for him to bear. He spoke of the terrible weight of being a champion. He was bitterly criticised by strutting macho columnists and commentators. What a wimp! He’ll never get anywhere in this game!

Sampras was always a sensitive toughie and it took him three years to get over the second impostor. He didn’t win another title in a grand-slam tournament until 1993. He then proceeded to add 12 more, making 14 in total, the best in history. All of which goes to show that the best can suffer from the second impostor, and that the best can get over it.

Perhaps the worst thing about the second impostor is the way that victory becomes, in a sudden, strange and magical way, so gloriously easy, as if you were taking part in a ritual, in a glorious trance, while your opponent somehow acquiesces to your whims and your desires.

Next time you play, you discover that sport is as difficult as it always was, that the glory was a one-off, that you must now go back slumming into the deep and dirty parts of yourself in search of victory. And maybe you don’t want to go there again.

Maybe you are satisfied. Maybe your thirst has been slaked. Maybe you simply don’t have that desire to go back and seek those extra 12 grand-slam titles. Maybe you don’t have that desire to go back into the boat again and seek a fifth quadrennium of suffering and pain and ultimate victory. Perhaps victory, of all of those things, is the last thing you can face.

Disaster destroys teams and individuals. But not half so well as Triumph.