But, what is the identikit picture of an assistant manager?
The Hoops boss had no hesitation in picking Johan Mjallby to stand by his side when he was handed the chance to manage the Parkhead club in March 2010.
But, with the Swede serving his notice, all eyes are on who Lennon selects to fill his not-inconsiderable boots.
At any club, having a trusted No.2 is essential. At Celtic, where the pressure and scrutiny is more intense than at any other club in the country, that is multiplied many times over.
Gordon Strachan - who brought Lennon into the management team at the club when Tommy Burns took ill in 2008 - knows that only too well.
From his first days as a player-manager, at Coventry in 1996, he leaned heavily on Garry Pendrey, who followed him to Southampton, Celtic and finally Middlesbrough.
They not only shared a birthday, but also a philosophy on football, and managing players.
Not that Pendrey was any kind of yes man. That would have defeated the purpose of his presence alongside Strachan.
The man who won three SPL championships with the Hoops and led them to the Champions League last 16 for the first time explained: "As a manager, it is great to have an assistant like Garry because there are times when they are there to make you think.
"They make you think of alternatives: They make you think about consequences.
"At the end of the day, they don't tell you what to do, and it is still up to you as manager.
"But, they have got to be 100% behind you because, if they are not, the players can sniff that.
"They can suss if the assistant is not backing what the manager is doing completely.
"That would then cause a problem in the dressing room because players can play on that and use it as an excuse.
"Your assistant has also got to be like a psychologist, because they have got to speak to you when you are down.
"You have to do most of the picking yourself up, but you do need a gee up now and then from the people round about you.
"Obviously, they also need to understand the game. And they have to be that link between the manager and the players.
"For that to work, the players must respect them as well."
Strachan admits Lennon is entering what, for him during his club career, were uncharted waters in his quest to find a replacement assistant.
"Garry went everywhere with me," he explained.
"Ron Atkinson brought him to Coventry at the same time as me when he was changing his backroom staff.
"I quickly discovered Garry was a knowledgeable man, unflappable. Nothing bothered him. He never brought anything into the training ground that would affect me.
"Garry was also great after games. He could go into the opposing manager's office, and you would never know if we'd won 6-0 or lost 6-0, which was great for me."
Strachan continued: "The only time I had to find another assistant was when I took over as Scotland manager.
"I asked Garry to join me, but he wouldn't come because he believed the Scotland team should be run by Scotsmen.
"So, the invitation was there, but he wouldn't accept it. He felt the same about England, that they should have an English manager and the backroom staff should be English, too.
"When you are talking about someone with principles, that is the type of man you are dealing with, and the kind of man you want by your side."
Strachan remains a close ally of Lennon, and an experienced voice at the end of a phone any time the current incumbent of the Parkhead hot seat seeks advice.
However, he does not expect to be asked to nominate anyone to replace Mjallby because he reckons Lennon will already have made contact with that person.
"I don't think there will be a shortage of applicants," said the 57-year-old Scotland boss.
"But, I don't think it is about waiting for applicants.
"Neil has probably already bumped into that person, at whatever occasion, coaching seminars, somewhere like that.
"Or maybe it has just been when he has been talking to people about football and thinking: 'I like what he could bring to the table to help me out here'.
"I don't think it's an interview process, as such. Neil will just think who has helped him in football, and who can deal with Neil as well."
Mjallby is the second of the four-man team assembled when Lennon took over the club in 2010 to leave, Alan Thompson having his ties severed for very different reasons two years ago.
Only Garry Parker of the original support team remains alongside Lennon, though Danny McGrain has since been promoted from the Development Squad.
Strachan is not sure it is a four-man job, and said: "In my opinion, three was always enough, really.
"I know that's not everyone's idea of a management team. But to my mind three is enough to make you think, whereas four starts to get a bit complicated.
"I don't count the goalie coaches in this because they do their own thing. So, for me, three is enough."