He had just watched his side come back from 2-0 down in the first leg of their Champions League play-off match to defeat Shakhter Karagandy 3-0 and progress to the group stage.
Having exploded in sheer relief as James Forrest scored the vital third goal a minute from time, Lennon now had to face the assembled media to discuss the match.
However, he had to wait as the Shakhter coach Viktor Kumykov had reached the press room first and was still bemoaning what he perceived to be their misfortune in being knocked out.
In the minutes he was kept waiting, Lennon became more and more agitated.
Instead of accepting the congratulations of those around him, he let his guard down and gave vent to his innermost thoughts.
The gist of what he said was that, over the course of the previous two seasons, he had brought in £50million to the club through two qualifications for the Champions League - including a run to the last 16 - and the sale of some of his very best players, including Victor Wanyama and Gary Hooper.
Yet, he kept repeating, he did not feel he had had any support.
By the time he actually got into the media room, he had calmed down - but only slightly.
There, the withering observation was toned down, marginally, but, the unhappy sentiment could not be disguised.
In hindsight, it was the moment Lennon knew he could not continue to operate under the conditions the current managerial position at Celtic demands.
His side had come perilously close to missing out on the qualification which defines Celtic's every season.
And, year upon year, in a position of diminishing resources, pulling off this particular trick was going to get harder and harder.
The achievement of reaching the last 16 had been as welcome as it was unexpected, given the previous two campaigns of this inexperienced group under his charge in Europe.
But for that team it was very much an over-achievement, with them punching well above their weight.
It had also set an unfair level of expectation, and would make any season they failed to get into the group stage, at least, deemed a failure.
This six-game tightrope at the start of every season had no safety net, and a fall would do immense damage to the reputation of a young manager who is ambitious in the extreme.
Witnessing Lennon's pent-up anger that night after the Karagandy escape act gave a glimpse into his soul - and an insight into his future.
He knew he should have tried to exit after the last-16 season, and that he had had a narrow escape in the following qualification games.
With the championship Celtic's before a ball is kicked each season, it is the European stage on which Lennon would always be judged.
To even get in on act one, he had be allowed the resources to ensure safe passage through two qualifying rounds and a play-off.
Sure, this intelligent man fully understood the club's policy of selling their best players for profit, but he had to wait to see if they were into the group stage and could bank Uefa's big cheque before they would allow him to make last-minute additions to his squad.
Some signings could be made early in the transfer window to get squad size back up, but their cost reflected how speculative those signings tended to be.
It irked Lennon, as did the club's failure to follow his request and go the extra mile to retain Hooper.
And, while he acknowledged the need for the club to follow this business plan, his true feelings and frustrations began to surface more regularly.
After a game at Inverness in late December, and in what was clearly a pre-conceived plan, he dropped the same comment into each of the seven interviews he had to carry out, for TV, radio and written press.
His point was that the club had sold £20m-worth of talent in the summer, but had not spent the same kind of money replacing it.
Another indicator he felt he had not only brought back the thunder to the club but was increasingly feeling he was having to pass wind against it was the repeated reverential references to Sir Alex Ferguson, the man who can be king-maker in England, his advice sought by so many owners and chairmen in the market for a new boss.
Lennon also made more and more appearances on TV programmes which would receive a wide audience down south, with his erudite and analytical appearances on Sky's Goals On Sunday and BBC's Match Of The Day particularly eye-catching examples of how impressive he can be.
Lennon knew the image he had to overcome was the snarling, finger-pointing dervish, at war with authority, figure he had cut on occasions during his formative years as Celtic manager.
They were the pictures and video footage most often used when anything about him was being discussed.
He felt it portrayed an unfair and inaccurate impression of him as a man and a manager, certainly not one which was going to get his phone ringing with job offers.
Lennon had endured more than any human being could reasonably be expected to do, with threats to his life and the well-being of his family in a hate-filled period soon after he had taken over from Tony Mowbray.
He also did not receive the credit he deserved for getting on with the job against this deeply-distressing backdrop.
But any sympathy was diluted by the ill-judged-but-often-repeated opinion he somehow "brought it upon himself" because of the character he was.
Lennon managed to shrug this off and, thankfully, for the past couple of years has seen the focus on him centred on what was happening in terms of his football team, not his personal life or touch-line behaviour.
He led the club he had served so well as player to a hat-trick of championships, and two Scottish Cup victories.
Of course, given the financial advantage they hold over every other cub in the country, it could and should have been more.
However, with Europe so important to the club, retaining the title and the qualification place for the Champions League that goes with it was always the priority, and the focus for every campaign, which could distract them in other competitions.
For Lennon, given the financial restrictions under which he had to operate, it was no longer the challenge he wanted, hence the decision to leave the security of his 12-month rolling contract and make himself available to anyone looking for a bright, ambitious manager.
It was inevitable, with Johan Mjallby's departure a signal it was coming. The only real surprise is it did not happen a year earlier.