Lennon admitted it was difficult to entice players to the play in Scottish Premiership where the demotion of Rangers from the top to bottom division of the league has left Celtic in a different class to the rest of the field.
"Some of them want to progress their careers, may be outside Scotland, and it's difficult to stop that progression," Lennon said after Wednesday's 2-0 defeat.
"We'll see how they are at the end of the seasons, we still have a championship to win and the Cup but this has been an incredible experience for them."
Lennon said the prospect of another Champions League campaign might help him keep players at the club.
"We probably won't know until next season," he said. "It would be a travesty for these young players not to progress after having achieved so much and played against some of the best teams in the world."
The highlight of Celtic's campaign was the 2-1 win over Barcelona in November which ensured they made it through to the knockout rounds and evoked memories of their greatest triumph of winning the 1967 European Cup.
"You always want more," said Lennon. "I think over the two games we played very well, we are just a bit short in some areas."
"The difference is that there is £100 million behind most of the other squads in the last 16, but we've shown that you can play in the Scottish Premier League and you can compete in the Champions League."
Celtic had to battle through two qualifying rounds even before they made the group stage with their campaign starting on in August when they beat HJK Helsinki 2-1 at home on their way to a 4-1 aggregate win.
They also saw off Swedish side Helsingborgs 4-0 on aggregate and were expected just to be cannon fodder for the other three teams in Group G.
They began the competition proper with a 0-0 home draw against Benfica before going to Moscow and beating Spartak 3-2 on their own patch, their first ever away win in the Champions League after 19 attempts.
Three weeks later they were only minutes away from drawing in Barcelona, taking the lead at the Nou Camp through Giorgos Samaras early in the game, before losing 2-1 to Jordi Alba's last-minute winner.
Two weeks after that came the highlight of their season, a 2-1 win over Barca at Parkhead where goals from Victor Wanyama and Tony Watt gave them a 2-0 lead before Lionel Mess scored in the last minute for the visitors.
Despite losing to Benfica in Lisbon, the city where they won the European Cup in 1967, they beat Spartak 2-1 at home to ensure their qualification which Lennon simply described as "a momentous achievement."
Celtic, 16 points ahead of the chasing pack in the Scottish Premier League, will wrap up their 44th title success in the next few weeks and be back in the Champions League again next season with the added pressure of trying to emulate this season's level of success.