The Hoops manager has admitted his transfer window plans will change if his side qualify for the competition’s group stage and whether he can raise funds through player sales
If the Hoops fail to qualify for Europe's biggest competition, however, they will need to sell players before they can buy, says the Northern Irish manager.
"The extent to which we can spend will depend if we can bring capital in from sales as well," Lennon told Sky Sports.
"If we get into the Champions League, and it's a big 'if' we'll have two days of being very busy. If not, if we do sell a player, there will be funds available for freshening up."
Celtic kicked off their Scottish Premier League season on Saturday, when they narrowly overcame a strong Aberdeen side thanks to a slip up from the Reds keeper.
He added: "We have good quality in the squad, but it's always good to add a little jag here and there.
"I'd like to add one in defence and a centre forward if we can. We will see what happens."