The Scottish champions secured a 5-0 aggregate victory over Cliftonville on Tuesday, as goals from Efe Ambrose and Georgios Samaras made it 2-0 on the night at Celtic Park.
That win sets up a third qualifying round showdown with Swedish outfit Elfsborg.
Celtic reached the last 16 of the 2012-13 competition but Lennon knows that it will be a challenge to repeat the feat.
"It's a fantastic competition and one which went well for us last year but there's no guarantees we'll qualify this year," he said.
"We'll have to start really stepping things up in the next week to be ready for Elfsborg.
"We know how important it is, but I can't base my whole season on qualifying for the Champions League, I have to look beyond that as well."
The Northern Irishman also confirmed that chief executive Peter Lawwell had spoken to Nottingham Forest about the potential transfer of striker Gary Hooper, but Lennon reiterated the club's desire for the former Scunthorpe United man to stay.
He featured in the final 25 minutes against Cliftonville after recovering from a groin injury.
"I spoke to him today and asked him how he was feeling," Lennon added. "He said he could do with some game-time, and that's exactly what we did.
"He's not given me any indication either way, so no news is good news on that front. If I've got him here for the next week, I'll be delighted.
"It's a better squad with Gary in it. From our point of view we want him to stay, and if we can persuade him to stay we will do everything we can to do that.
"I think Peter was speaking to Nottingham (Forest) today to tell them that he's not for sale, or if he is for sale they are going to have to come back with a sizeable offer.
"He was excellent tonight and he has been for the last 12 or 13 months now."
