AS dress rehearsals go ahead of the crunch play-off meeting with Shakhter Karagandy, it didn't exactly follow the script.

Sure, Inverness Caley Thistle sat deep and frustrated Celtic, challenging them to break them down but remain alert to dangerous breakaways, as the Kazakhs will do on Wednesday.

But Terry Butcher's side took it a step too far by replicating Shakhter's two-goal lead.

The Hoops players did not need any further reminder of their fallibility at the back, nor, indeed, their inability to defend long throws with any degree of efficiency.

The simple fact is that, knowing how much bigger the mountain they already have to climb will become if the Kazakhs manage to get another goal to add to the two they scored in Astana, Celtic needed the re-assurance of a competent defensive display - and a shut-out - in their SPFL Premierhsip game between the two ties.

Falling two behind within 35 minutes to a good strike from Aaron Doran - a consequence of not closing down space - then a scrappy effort from Richie Foran - the result of failing to deal with a long throw-in - was not at all what the doctor ordered to cure the attack of nerves afflicting the Hoops squad.

They have every right to be jittery. There is so much on the line on Wednesday, and they look shaky at the back and less than on top of their game up front, relying on defenders Charlie Mulgrew and Adam Matthews to step forward and provide the goals which gave them a point against Caley.

Lennon has to find the elixir to put life back into their Champions League group stage challenge.

If not, the players and supporters will have to swallow the bitter pill of dropping to the Europa League.

Adding to the mix is the fact Lennon must wait to find out which of his ailing men he has available, with a treatment room full of attack-minded Bhoys, including Georgios Samaras, Kris Commons, James Forrest, Anthony Stokes and Derk Boerrigter.

All missed out at the weekend, while Beram Kayal limped off with a groin injury which has almost certainly ruled him out this week, and Virgil van Dijk was forced out after feeling a hamstring, an injury which will be assessed fully over the next couple of days.

Already concerned about the depth of his squad and desperately trying to add to it - though any new signings will not be eligible for Wednesday's tie - it adds up to one of the most important weeks of Lennon's roller-coaster managerial career.

He admits he feels the lows more than he enjoys the highs, and losing out to Shakhter would be a new depth plumbed.

The fans did their best to get behind them against Caley, especially when they were trailing.

But how much patience will be shown by what is expected to be a full house on Wednesday? And how will the players - on both sides - react to the demands being placed on them?

In all honesty, no-one knows for sure.

What Lennon does know is that his team struggled over the two ties against Elfsborg in the previous qualifying round, and have yet to show their best form this season.

The campaign is now five weeks old, so the excuse that all of this comes too early for them is wearing thinner by the day.

The play-off return against Shakhter will be Celtic's ninth match this season, and match fitness and sharpness should no longer be an issue.

Instead, focus and concentration appear to be what they are still trying to get up to the required level.

It was their undoing in Kazakhstan, and it was what put them behind the eight-ball again at the weekend.

Lennon was honest in his assessment of their afternoon's work, highlighting what they did poorly, and what eventually they did right.

He said: "I don't think we played well at all in the first half, but the team showed great character.

"We knew we were going to be a bit short in terms of attacking options, and that proved to be the case.

"However, we could have won it in the end. The second half was more like us, but, in the first half, some let the game pass them by.

"Scott Brown grabbed them by the scruff of the neck and drove them forward all day with a real urgency, which was lacking in the first half."

The fact the starting XI against Caley showed six changes from the side which played in Astana, most of that forced by injuries, did nothing to help settle the team.

For those who stepped in, hoping to stake a claim for inclusion in midweek, it was a mixed bag. Amido Balde had decent chances to score, particularly with headers, but barely worked keeper Dean Brill.

Tony Watt was much more lively than the Portuguese striker, but did most of his good work out wide when he was needed in the box.

Efe Ambrose partnered van Dijk in central defence, but brought no more solidity to the back line than the man he replaced, Steven Mouyokolo.

Lennon was preparing to bring the Frenchman on as a replacement for van Dijk midway through the second half but, at the last second, decided to put on Mikael Lustig to allow Mulgrew to move from midfield to central defence and Matthews to be released into a more attacking position.

This brought the hard-earned equaliser, due mainly to the fact Matthews was found by man-of-the-match Brown making a diagonal run infield rather than static in a wide position, like most of his team-mates.

If Forrest does not recover from his sciatica in time, Matthews may now find himself thrust into a right-midfield role against Shakhter, with a licence to drive at what will be a deep-sitting defence.

Tom Rogic was also given his opportunity to show he has something to offer against Shakhter, but it was his first start of the campaign and it showed.

Like so many, the young Aussie will be praying Celtic can get over this major obstacle and can look forward to another season of Champions League football.

But every one of Lennon's players will have to raise their game from what has been delivered to date.

They must regain the defensive soundness which saw them go seven qualifying and play-off games without conceding before they got caught napping in Astana, and rediscover the potency in front of goal which made them irrepressible through last season's qualifiers, play-offs and group stage games.

If not, the large trap door to the Europa League will open below their feet, and the fall will last for a very long time.