The shockwaves created by the defeat to Ross County in the semi-final of the Scottish Cup a few days earlier were still being felt.
The interim manager had made a terrific start after taking over from Tony Mowbray, putting the Hoops back on the winning track in the two games prior to them heading to Hampden.
But, that cup exit raised serious doubts about the rookie's qualifications to take on the job permanently.
Three championships, two Scottish Cups and a last 16 spot in the Champions League later, Lennon has answered all his doubters in spades - and in trophies.
As he settles into his fifth full season in charge - with preparations well underway after clinching the title in jig-time - Lennon recognises that looking long-term, but not losing sight of the present, is the key to being a successful Celtic boss.
So, while he is fresh back from checking on a few potential targets down south, the Hoops boss is also keeping a close eye on the rising stars "bubbling under" within the club's own academy.
The sight of Liam Henderson and Eoghan O'Connell following Darnell Fisher in making the step up from the Under-20s this season is proof that, not only is the development system in which the club ploughs millions working well, it remains a rich source of talent which the manager will continue to mine.
"The academy is important to me, because of the economic climate that we are in," said Lennon. "And we are pretty pleased with it."
The U20s had hoped by now to have joined the top team in adding another league championship to their trophy haul.
But after having Lennon as an interested spectator when they defeated Rangers at Murray Park, they have lost a couple of games to league leaders Hibs and then to Hearts to keep them in second place.
However, while the winning mentality is a prerequisite of any player hoping to make it at Celtic, Lennon accepts the academy's premier role is to drip feed players to the first-team squad.
"It is something everyone at the academy works hard at," said the manager. "When they see one of the players coming through, everyone gets a sense of achievement and pride.
"But what we want is not players coming up for one or two games, we want them to be part of the first-team set-up for the next three, four, five years. Darnell and Liam have done their chances no harm."
In an ideal world, Celtic would regularly be able to delve into the latest Quality Street Gang, that famous group of kids in the late Sixties which included Kenny Dalglish, Davie Hay, George Connelly, Danny McGrain and Lou Macari.
But, everyone accepts they were a one-off from a golden moment in time.
For too long, Celtic lost it's way, in terms of discovering and developing players from an early age then handing them a first-team jersey, preferring instead to buy players, and in so doing blocking the natural path to the top which their kids might have followed.
Now there is a hybrid approach, with scouting bringing in players from all around the world, but while still very young, and adding them to the local talent, which is introduced into Celtic training camps from the age of five.
It is inconceivable that, as well developed as the academy is, it will ever fully negate the need to go out and purchase players.
But, it is becoming a more integral and important facet of the business plan.
The more youngsters who can step up from the academy and become regular and long-term players in the first team, the more Lennon can focus on investing what funds he has at his disposal on the level of quality of player who might have been out of his reach if he needed to bring in five or six to plug gaps.
The manager explained the methodology applied when shopping for talent: "In terms of bringing in players from abroad, it's just trying to find players at a good price who will make us better.
"Virgil van Dijk certainly fits the bill on that, and Nir Biton showed, until his injury, what a good player he is going to be. Stefan Johansen is also playing very, very well.
"Derk Boerrigter has been injury-hit this season, and from Amido Balde and Teemu Pukki, there is more to come.
"Allied to all of this, we have a good core of British players, with Scott Brown, Charlie Mulgrew, James Forrest, Kris Commons, Fraser Forster and Adam Matthews. They are the ones who really keep the dressing room bubbly."
Precisely who will still be here when next season kicks off with the Champions League qualifiers in July - and who might have joined them by then - no one can say for sure.
Certainly, Lennon wants to add around four new faces, but is loathe to lose too many, though Georgios Samaras and a few others appear to be edging towards the door.
The manager has learned through the past four summers that anything can happen, with signing targets slipping through their fingers, and players already here lured away for the kind of transfer fees which proves the club's raw-talent- to-polished-gems signing strategy is working well.
But while he does not know who he will have available for these key opening games, Lennon does at least know where they will be taking place, Murrayfield Stadium.
He has been monitoring the laying of a new playing surface at the home of Scottish rugby, and is already looking forward to another first for the famous club.
Lennon said: "I've never been in Murrayfield, but certainly, the infrastructure and facilities look fantastic.
"They are laying a new pitch as well and we will need to go and train there and have a look at it to get used to the dynamics of the stadium.
"We will not know how we are going to react until we actually play a game there. But it's as good a stadium as we could probably get, under the circumstances."