But the Hoops boss believes it will be worth it – because it could culminate in a Last 16 place in the Champions League.
Lennon reckons facing Benfica – who are desperate for three points to keep their own qualification hopes alive – will pose an even bigger challenge to his players than Barcelona.
And he is no doubt the return of skipper Scott Brown plus Joe Ledley and Gary Hooper will be vital. As the buoyant Celtic squad prepared to fly to Portugal today, Lennon said: "This will be the toughest game of the group.
"Benfica will be very motivated to get the win. They are at home and have a proud record there. They are a real calibre Champions League team, and are going well domestically.
"They have some really good players, and, mentally, they are strong and strong defensively. So we are in for a long night."
However, Lennon trusts his players, and no one more so than Victor Wanyama who scored against Barca and continues to enhance his reputation as a midfield powerhouse, despite walking a suspension tightrope.
A booking tomorrow would rule him out of the final Group G game against Spartak Moscow on December 5, which could still determine Celtic's European fate.
But Lennon has no plans to tell the 21-year-old Kenyan to hold back against Benfica.
"He has just got to go out there and play his natural game and what will be will be," said the manager.
"For us, the beauty of the last game is that it's at home. If Barcelona beat Spartak in Moscow, we have got Europa Cup football at least.
"Then we can just throw everything into the final game against Spartak, if – and it's a big if – we don't get the result we want tomorrow."
A score draw could be enough to see Celtic through, but Lennon insisted: "I'm not setting the team out for a draw.
"What we have done in previous away games is create chances, and that has really pleased me. Maybe in years gone by we have not been as offensive. Now we've got players who can create, and that will be vital on the night."