Norwich City have already seen one bid for the striker knocked back and are believed to be readying an improved offer.
Lennon concedes that every player has their price and that there would become a point where Celtic would have to enter into negotiations.
He is, however, hoping that transfer talks can be avoided, with Celtic able to offer Hooper UEFA Champions League football and regular competition for silverware.
After seeing Hooper bag a brace in a 4-1 victory over Hearts on Saturday, Lennon said: "That will add a few million to his value.
"Listen, I don't have a crystal ball, I don't know what's going to happen in the next couple of weeks.
"I have made it clear, Peter Lawwell has made it clear and the board have made it clear that we are not selling him.
"However, everyone has their price. What Gary's price is will be down to myself and the board to decide if a club comes up with that figure. What we were offered on Thursday was nowhere near our valuation."
On the prospect of improved bids being lodged, Lennon added: "I'm hearing that they (Norwich) might come again, but good luck to them on that.
"He's already at a big club and playing in the Champions League. His ambition possibly is to play in the Premier League. He's good enough, there's no question.
"I am not going to stop any of the players' progress because I wouldn't have wanted that done to myself. But I'll do what I think is in the club's best interests.
"I am sure he's on the radar of plenty of clubs, it is just Norwich have come in first."