The Parkhead men trail their hosts at the top of Group G by two points after two games.
But few expect an away win, although Barca coach Tito Vilanova has a defensive crisis, with Daniel Alves, Carlos Puyol, Gerard Pique and Eric Abidal all expected to be missing.
Hoops boss Lennon acknowledged the size of the task in hand but is keen to ensure his players are in the right frame of mind.
He said: "It is exciting times for the players, club and the supporters.
"But we are not here for a holiday. We are not here as tourists.
"We are going to be in for a tough 90 minutes, but we want Barcelona to be in for a tough 90 minutes.
"We need character and mental strength and allied to that, the players need to play at the peak of their abilities to overcome what is probably the best team in the world at the minute."
However, Lennon admits Celtic's first away win in the Champions League against Spartak Moscow earlier in the month, where Georgios Samaras headed a late winner in the 3-2 victory, has taken some of the pressure off his side.
He said: "What we have done is give ourselves a platform. Maybe we didn't visualise getting a result in Moscow but this is the ultimate test, away from home against Barcelona.
"We haven't budgeted for anything out of this game but who knows?
"The players are young and fearless. There is a bit of naivety about them at times but there is plenty of international experience, we saw that in Moscow."
"We are in confident form, we got a great result against Spartak in the last game so we have nothing to lose."