It was just last November he sent shock waves around the world by deploying smash-and-grab tactics which saw his side defeat Lionel Messi and Co. at Parkhead.
It's a mere 12 weeks since he sent his Bhoys back out to face the La Liga champions in their most recent meeting.
As a player, he pitted himself against the Catalan giants no fewer than four times, winning once, losing once, and drawing twice in the Nou Camp.
Yet, as the Hoops boss prepared to fly out to Spain today for the next Barcelona v Celtic clash, Lennon admits he doesn't know what to expect.
He had hoped the closing match in Group H would be an opportunity to record another memorable result which would allow his team to progress deeper in this year's Champions League or even parachute down to the Europa League.
Of course, that ship sailed when Celtic were left marooned by defeat to AC Milan last month on the same black night Barca lost to Ajax in Amsterdam.
That combination of results means tomorrow's tie is now a dead rubber, in terms of Celtic's interest in Europe for this season.
But Barcelona still need a point to ensure they top Group H and go into the last 16 draw with all the advantages that brings.
Their form of late has shown their early-season invincibility - when they went 20 games unbeaten in all competitions - has come to an end, coinciding, not surprisingly, with the loss to injury of Messi.
However, back-to-back defeats by Ajax then Athletic Bilbao have been followed by a 4-1 victory at Cartegena in the Copa del Rey.
All of which has been closely followed and examined by Lennon, who admitted the patchy form of Barca allied to the positive reaction of his own side since losing to Milan makes predicting what will happen next a mug's game.
"I don't know what tomorrow night is going to bring," said the Parkhead boss. "We could play well. We could get beaten heavily.
"I don't know what the fall-out of the match is going to be. But, certainly, we are concentrating now on improving all aspects of our game."
As well as Celtic have been playing - as the huge margins of victory over Hearts and Motherwell underline - Lennon has continued to revise his tactics and swap his personnel to keep everything fresh, and opponents guessing.
Perhaps this is a reaction to the criticism his side had become too predictable. Or perhaps it has been the result of players returning from injury and suspension while others have been forced out of action.
Whatever the reason, despite scoring 12 goals for the concession of none in the last two outings, Lennon is expected to ring the changes again in the Nou Camp.
"The formation we are using seems to suit us," he said. "With James Forrest having been out, there has been a lack of width, or lack of wing play, anyway.
"The full-backs are getting forward, but you have to earn the right in the midfield, and we did that at Fir Park on Friday.
"Of course, it will be different at the Nou Camp.Barcelona still need a point to win the group, but they never play for a draw, do they?
"I don't know how strong they will go with their line-up. They made a lot of changes for the Ajax game in Amsterdam.
"But no matter who we face, we are playing Barcelona in the Nou Camp, and that is quite a daunting prospect.
"It's not a nothing game for us. We might never get the opportunity to do it again, and we want our players to go out and play as well as we can.
"If the last two games are any reflection on it, then we will be okay."
There is a school of thought that, having seen their chances of progression disappear by matchday five, Celtic can cut loose and play with freedom against Barca.
The wisdom of such an approach is questionable as no-one at Parkhead wants to allow naivety to be their downfall and permit what has been a campaign which started with so much promise to end with a bloody nose.
Besides, Lennon simply cannot agree with the suggestion this is a nothing game for his side.
"There is still money at stake, in terms of points and bonuses for the players," he points out.
"But it is pride more than anything, and the opportunity for them to play in a great stadium and for me to coach in a great venue. That is still something for us all to really relish."
Lennon is also wary about the notion Messi-less Barcelona might not be at their very best. With the likes of Neymar stepping into the breach, and Xavi, Andres Iniesta, Gerard Pique, Pedro and Alexis Sanchez still flying the flag with distinction, your guard must be maintained at all times.
Lennon is dismissive of Barca's recent hiccup and pointed out: "I am pretty sure they are still top of the league in Spain, despite losing the other weekend.
"I think that was their first domestic defeat of the season. So they set the bar quite high."
Which is precisely what he has demanded his own side attempt to do. He has been delighted by the character shown since the disappoint-ment of going out of Europe, and the run of results they are now putting together confirms what a good place, mentally and form-wise, they now find themselves in.
After tomorrow night, the focus will be fully on extending their seven-point lead in the race for the title and the sole Champions League qualification place which comes with it.
Lennon said: "The Champions League is about to disappear for us and we can solely concentrate on the league. This time last year we put together a very good run, and we are hoping to do the same this season.
"We want to preserve our unbeaten run, but, more importantly, we are still looking at the performances and we want to find that real consistency. If we do that, then it is going to be difficult for teams to stay with us."