THE lexicon of football is scarred by the terms hoodoo or bogey.

Sportsmen and women, aware of the capricious nature of their trade, are routinely superstitious so Celtic players will bridle at the suggestion that there is a Hampden hoodoo that haunts their every visit to the national stadium.

Yet there is evidence that the champions have underperformed on the south side of Glasgow. They have won on only four of the past nine occasions they have played at Hampden, although they did lift the Scottish Cup there just under two years ago. However, the failures exist and they have come when Celtic were heavy favourites to beat Ross County, Rangers, Hearts, Kilmarnock and St Mirren across the two national cup competitions.

The question is why. Is there a specific reason for coming up short? Is it a matter of taxes, style or psychology? Is it a combination of all three? The matches may be best examined initially in isolation.

The Ross County game featured a demoralised Celtic facing a side that was prepared to pass relentlessly and cleverly. Neil Lennon, the caretaker manager, saw his side outclassed and outfought and vowed to change the mindset and the make-up of the team he had inherited from Tony Mowbray.

The Rangers match, in contrast, came as a vibrant Celtic seemed to have seized the mantle of dominance from Walter Smith's side. Rangers were properly apprehensive approaching the Co-operative Insurance Cup final but goals from Steven Davis and Nikica Jelavic exploited a vulnerability in the Celtic defence. The winner, in extra time, was a masterclass in how not to defend a free-kick.

The run of defeats by Kilmarnock, Hearts and St Mirren contain further painful lessons for Celtic. Kilmarnock placed an extra man in midfield and Celtic lost the obligatory bad goal from a defensive standpoint. The Celtic support screamed for a penalty when Anthony Stokes fell late on but Willie Collum waved away appeals. These howls of anguish were also aimed at Kelvin Wilson, who allowed Dieter Van Turnhout the freedom of the six-yard box to score the only goal. Kilmarnock were composed, organised and generally brave on the ball but claims that they outplayed Celtic can be countered effectively by the observation that Cammy Bell, the Ayrshire side's goalkeeper, was named man of the match.

The Hearts semi-final was marked by poor officiating. Euan Norris gave a highly contentious penalty and the fourth official should have advised the referee to send off Ian Black for a late, reckless tackle. However, Celtic's equaliser was offside so this was equal-opportunity incompetence. Celtic, who dominated the first half, were undone when Paulo Sergio, the Hearts coach, introduced Craig Beattie at half-time to unsettle the Celtic defence.

The St Mirren match emphasised the importance of putting Celtic on the back foot. Danny Lennon's side started vibrantly and were worthy winners. There have been justifiable accusations of complacency against the Parkhead side in the Ross County and St Mirren matches but other factors are conspicuous in the run of defeats.

First, Celtic's opponents have gained a measure of control in midfield where they have generally deployed five midfielders. Lennon's side, too, have been profligate in front of goal. Crucially, Celtic have lost the first goal in all the matches they have lost.

The best advice to Jackie McNamara's Dundee United side on Sunday would be to score the first goal. This is normally a statement of the bloomin' obvious but it would increase the pressure on a Celtic side who might fear another loss.

"Patterns emerge in sport," said Donald MacNaughton, the Scottish sports performance coach, whose 12 Hidden Laws of Performance has become a bestseller. "There is no doubt that sportsmen and sportswomen can reflect negatively on past experiences. It is a human reaction. They can not stop their minds receiving the signals that they have been here before and it has ended badly. They must recognise those thoughts then break them up with positive affirmation."

So would he advise McNamara to raise the question of a hoodoo? "Absolutely," he said. "He must tell his players to create the situation of doubt in the Celtic players. He must remind them that Celtic have been beaten before at this stage by teams that Dundee United have beaten."

So what about Lennon? What should the Celtic manager's approach be? "He will remind his players of how good they are. The league table shows they are the best team in Scotland; he will be telling them just that. He knows, too, he has led a team to a Scottish Cup triumph at Hampden. The players must be brought to a situation where they are prepared to enjoy the occasion and are ready to react positively to the pressure. Neil Lennon will be reinforcing to his players that they are the best and to go out and show it."

But MacNaughton, who has worked extensively with football coaches, believes both managers will concentrate on the specifics of the game rather than addressing hoodoos, or lack of them. "Modern managers have to concern themselves with the detail," he said. "There will be more talk of set pieces and who players should pick up, or whatever."

The question of hoodoos might be overplayed but Celtic must win on Sunday to avoid another airing of the curse of Hampden and how it diminishes the champions.