ANYONE seeking a summary of Celtic’s problems in Europe this season need have looked no further than Scott Allan’s chequered contribution in their game against Ajax last night. A couple of promising passes, a few aesthetically pleasing moments that gave grounds for optimism - and then a split-second lapse of concentration that led to the Dutch team’s winning goal.

It was an individual error, but one which was emblematic of the team’s failings as a whole, so it would be unfair to be over-critical of the substitute. From manager Ronny Deila’s point of view it would also be counter-productive, because at least Allan showed, on just his fourth appearance for the club, that he has the ability to make a positive difference at this level.

The midfielder was outstanding at times in the Championship last season, but there was an obvious question to be asked about how well he would perform against more able opponents, as well as about his tendency to drift out of games when things were not going his way. Hibernian’s improved form in the same division without Allan this season has led some observers to infer that he is over-rated, but those few tantalising glimpses against Ajax produced hope for a brighter future. Scottish football will be a lot poorer if he fails to realise his considerable potential.

Of course, you could say the same thing of several other members of the Celtic squad. Leigh Griffiths, for example, under-performed badly last night and took to Twitter to blame himself. Such frustration was understandable, perhaps commendable, but Celtic’s problems are bigger than just one misfiring striker. Like Allan, Griffiths is capable of a lot more, and it would be a mistake to demand that he carry the can for his team’s defeat.

Having said that, time is not entirely on the side of those two when it comes to realising their promise. Allan celebrates his 24th birthday tomorrow; Griffiths turned 25 in August. Gary Mackay-Steven, incidentally, is the same age as Griffiths, and Stuart Armstrong is 23. None is yet at the age where players are normally thought to be at their peak, but they are all a bit long in the tooth to be regarded as promising youngsters.

But for the injuries that ruled out Scott Brown and Kris Commons, among others, not all of that quartet would have been involved against Ajax. But they are part of the Celtic squad, and as such their form - or lack of it - has to be a matter for Deila. If one is below his best it might be seen as an individual problem, but if all of them are failing to realise their potential, the manager has to take responsibility - either for being unable to help them develop as a good coach should, or for failing to realise that they were not good enough to be part of his squad in the first place.

If the Celtic board really do decide to stick by Deila for another Champions League qualifying campaign, they will surely first need to see some evidence that he is taking his squad in the right direction. Given the relative lack of domestic competition, winning the league and one or two cups this season will not be enough. The Norwegian needs to win them in style - and to do that he needs to get players such as Allan and Griffiths, Armstrong and Mackay-Steven playing with more assertiveness and maturity. In short, he needs to get them to grow into the jersey.

One worry is the failure of three of them to shine in England, when they were out of their comfort zone. Griffiths did not settle at Wolves. Allan had a frustrating two-year spell as a West Brom player, in which he was loaned out to four other clubs. Mackay-Steven had two years at Liverpool and another two at Fulham before kick-starting his career in Airdrie.

You always worry that players who have had such experiences will never quite become as good as they could be. Again, sometimes the problem may lie with the individual, but if a number of members of the same squad are exhibiting the same symptoms, it is up to the man at the top to produce the remedy.

Then again, as things stand there is an argument that Deila should be seen in a similar light. And that, having been successful in his own country but proved unable to replicate that success in Scotland, he will in years to come be known as the Harald Brattbakk of management.