Now, as Celtic veer dangerously towards the exit ramp for the Champions League, the man who stepped down as Hoops boss at the end of last season can empathise with how his successor, Ronny Deila, is feeling.
The man who led Celtic to consecutive group stages, and the last 16 to seasons ago, recalled how it all went horribly wrong for him when he took over the wheel from Tony Mowbray in 2010.
With the club's biggest stars regularly being sold over the past few summers, and little investment in quality, Lennon knows how tough it is going to be for Deila to turn things round after the heavy defeat in Warsaw in Wednesday.
But, he is backing the Norwegian to get it right. It might just take time - the most precious commodity of all for a Celtic manager.
Lennon said: "There's always a transitional period at a club like Celtic.
"Ronny's not really had enough time to work out what his best team is yet.
"It's always good to freshen things up, and there's no better time to do it than this time of year.
"The important thing is they can hold on to some players as well.
"But, if there's no Champions League football, that's going to be difficult."
Southampton are expected to submit their improved offer for Fraser Forster over the weekend, while they have joined Sunderland and Swansea in vying to buy Virgil van Dijk.
An early exit from the Champions League - and the loss of the millions that would mean - will accelerate their departure.
But Lennon has not given up hope they can still retrieve the Legia tie.
He masterminded the comeback from 2-0 down in the first leg of their play off tie against Shakhter Karagandy 12 months ago and said: "They're not out of it by any means, but they've got a mountain to climb.
"I know it's Murrayfield, but still, anything could happen.
"It's disappointing, but not insurmountable."
Lennon will be watching the second leg closely. But, though still looking for his next management post, he has no regrets about calling time on his four years in charge of the club.
"I had my own reasons for leaving, and they were varying," he explained.
"I had 14 great years as a player, coach and manager. It was time for me to move on.
"The club understood that, and I had great people in the background working with me."
Having helped bring in around £50milliion from player sales and Champions League participation over the final two years of his first management job, the club's unwillingness to reinvest much of this back into acquiring quality replacements was one of the reasons Lennon stepped down.
He remains coy on this, however, and said: "It wasn't the sole reason, but it may have been one of the reasons."
Lennon is confident Deila knew the financial restraints before he took the job, and backs him to get it right in the end.
He said: "There's no need to panic just yet."