When everyone trooped on to the flight home from Denmark with Celtic on Tuesday night, the little man sitting in the front row already had his face buried in a book on his lap.

Gordon Strachan, his reading glasses attached, appeared to be doing a fair impersonation of someone with his head bowed in shame.

Things weren't quite that bad for Celtic in Aalborg, though they were bad enough. The hunch persists that the Danish side is not as good a team as Celtic, and certainly not with half the wealth - for what that is - of the Scottish champions. Therefore, why had Strachan's team been beaten to the consolation Uefa Cup spot by a side that currently sits seventh in the Danish league?

For Scottish football, there is now the wider question of our game's sudden plunge into a depression in the context of Europe, given the humbling of Rangers, Motherwell, Hibernian and now Celtic in the early furlongs of this 2008-09 season. It is only six months since Rangers were in the Uefa Cup final, and Celtic have reached the last 16 of the Champions League for two successive seasons, so the bleak, knee-jerk stuff should perhaps be kept in check. Nonetheless, something is badly amiss when such fodder as FBK Kaunas and Aalborg do what they have done to Rangers and Celtic this season.

Luck is always a factor in football, and Celtic have had little of it in their group E adventure. Quite apart from Barry Robson's missed penalty against Aalborg at Celtic Park in September - the very moment that kicked off this whole Celtic drama - Scott Brown also scored a perfectly good goal in that game, which the match officials erroneously ruled out for offside. There were also the two offside goals that helped Manchester United sweep past Celtic at Old Trafford, just when Strachan's men were holding United at bay.

And yet, citing too much poor fortune eventually sounds like bleating and is unconvincing. Was it bad luck that made Georgios Samaras and Shunsuke Nakamura miss very good chances in Aalborg? Was it bad luck that made Celtic allow the Danes to come back at them in the second half and cause anxiety around Artur Boruc's area, eventually leading to Gary Caldwell's own goal? The truth is, Celtic invited their own misfortune because, once again, they weren't good enough.

Their much-cited woeful away record in Europe also has elements of bad luck about it - in Munich, Lyons and Turin to name but three places Celtic could have fared better over these years - yet the same principle applies. Bad luck cannot be cited as a main cause of Celtic's downfall. If the Scottish champions cannot learn how to keep a clean sheet, then what else is to be expected?

The presence of Strachan remains intriguing in all this. What will his mood be? He is now in his fourth season at Celtic Park - getting close to that threshold when a manager of his pedigree feels it is time to go and taste England once again.

It happened to Martin O'Neill after his five dramatic years in Glasgow, notwithstanding that it was his wife's illness that finally made O'Neill bow out of Celtic. The time, inevitably, is edging closer to Strachan's departure from Celtic.

Perversely, given his subdued demeanour on the plane home on Tuesday night - head down, quiet, sober in tone - the one man Celtic fans cannot really criticise is their manager. In any game or season a coach will make mistakes but Strachan's haul of three successive titles and two last-16 Champions League spots is the stuff of admiration, not condemnation, in Glasgow.

That backdrop alone, though, will only make the Celtic manager agonise more over the way his team have been turfed out of Europe.

Without European football, Strachan will not be looking forward to the days and weeks ahead. The job goes on and the games will come but imminent glamour is no longer on the horizon. There will be no Fiorentina, no Dynamo Kiev or - best of all - Zenit St Petersburg and Dick Advocaat coming to Celtic Park in early 2009. Craig Brewster's Caley Thistle, on the other hand, arrive at Celtic Park on Saturday.

The one aspect that will rekindle the excitement of Celtic and their supporters will be a strong Rangers. The last thing the Celtic Park hordes will want to feast on are these long, dragging affairs against Falkirk and Hamilton Accies as they bear down on another title. If Rangers, however, make a fight of it, the effect will be to energise Strachan, his players, and the whole Scottish scene.

Celtic, however, will not look back lightly on their submission to a moderate Danish side in this season's Champions League.