A host of Premier League clubs have already been credited with an interest in the 24-year old with Norwich City even tabling a bid which the Hoops rejected.
Hooper scored a brace in Celtic’s 4-1 win over Hearts on the weekend and Lennon feels his number one scorer could be the subject of further offers from top flight English clubs this winter.
"That will add a few million to his value,” he said.
"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, (chief executive) 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 (reportedly £5million) on Thursday was nowhere near our valuation."
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."