The Hoops manager was close to blowing a fuse when he watched them play without power against St Johnstone – and got wired into his men afterwards.
His vast experience as a player, and crash-course in crisis management since he hung up his boots, has left the Northern Irishman in no doubt that a strong mentality and professional approach are not optional depending on the day or the game.
Rather, he insists they are pre-requisites every time a player pulls on a Celtic shirt.
"You can't just turn it on and turn it off, and we have told them that, time and time again," said Lennon.
"But there was just a lack of cutting edge and a lack of endeavour from us."
The hope is that the threat to reconsider his team for Wednesday's Champions League group opener against Benfica on the back of Saturday's lacklustre 2-1 defeat at McDiarmid Park is still resonating with the men who let Lennon and the supporters down so badly at the weekend.
Injuries and the continuing complications associated with obtaining a work permit for Efe Ambrose will temper the manager's ability to make changes.
But it will be a change of approach and commitment rather than personnel which will be most important on Wednesday.
Having taken the lead against Saints after only four minutes, when Kris Commons finished a good move involving Scott Brown and Gary Hooper, the lights went out right across the Celtic team.
Poorly defended goals from Gregory Tade and Rowan Vine understandably left Lennon incandescent.
The sight of Celtic lying fifth in a league which many believe is theirs by default will have done nothing to calm him down.
It must surely act as the necessary wake-up call to the players.
Sure, there is plenty of time to repair the damage from taking just eight points from the opening five games. However, it could take a lot longer for the damage currently being done to the reputation of the club to be rectified.
Lennon has a long memory, and the pain which he suffered at the start of last season when his side struggled to find any consistency, forcing the manager and fans alike to watch Rangers build a healthy lead in the title race, is never too far away from his thoughts.
It took a brave performance against Rennes in the Europa League to kick-start the comeback that year.
Lennon will look for a similar performance on Wednesday, though even that will not mollify a man who demands the standards he has set for his side are maintained at all times, not just on big occasions or when it suits.
The discrepancy between the performances in the Champions League qualifiers and what has been served up in the defence of their SPL title is simply unacceptable, and the blame lies squarely at the feet of the players.
Lennon trusts they do not have to find out the hard way that it is not possible to turn in a sub-standard performance one day then expect to turn on the form four days later, simply because the strains of the Champions League theme is filling the air.
It is only by playing consistently well every week that the confidence and momentum required to take into games against Europe's elite can be secured.
It appears too many Celtic players are failing to grasp this fact of footballing life, and on Saturday the evidence was that they believed a dramatic late goal – as was scored at Dingwall - would arrive if they hung around long enough.
The error of their thinking has been hammered home now, and a positive response is not only expected, but demanded.
If they are suffering from a European hangover, the boss is promising he has some pretty unpleasant medicine available as a cure.
Reflecting on as poor a display as he has seen from his side for a year, Lennon emphasised that if any minds had been allowed to wander going into midweek, it was against his command.
Lennon said: "All my focus was on Saturday. I had not spoken to the players about Benfica.
"I am not passing the buck. We are all culpable, but that performance was tepid, it was dull, it was lacking urgency and it was certainly lacking quality in a lot of areas."
Most disconcerting for Lennon was the fact that, when his team, which saw Miku make his debut alongside Hooper, conceded an equaliser, there was still more than three quarters of the game to go.
When more sloppiness allowed Saints to take the lead, seconds after another new Bhoy Lassad Nouioui came on, there was another 12 minutes to play, yet no one stepped up to the plate to drag the team back into the match.
"We gave them all the warning shots before the game, then we gave the more at half-time," revealed Lennon.
"We had a couple of decent chances to score, particularly in the second, and the goalie has made a great save from Tony Watt at the end.
"So, I can't criticise them for not creating chances, but I can criticise them for not working the ball well enough, and not defending well enough in crucial areas. I thought we were a bit soft."
Only Wednesday will tell if Lennon's stiff rebuke will alter this concerning condition.