Lennon reluctantly confirmed the development after reports emerged in England of a £5million offer from the Barclays Premier League club.
Hooper has so far resisted persistent attempts by Celtic to extend his contract beyond the end of next season, but the club are in no hurry to cash in on the prolific forward as they chase four trophies, including the Champions League.
Lennon had yet to talk directly to Hooper when he confirmed the bid had been rejected, but made his position clear at the pre-match media conference ahead of Saturday's Clydesdale Bank Premier League visit of Hearts.
"Our case is simple - you are not going," Lennon said.
"You have got a year and a half on your contract so you're a Celtic player."
Lennon, whose team face Juventus in the last 16 of the Champions League next month, added: "The bid has been rejected. We had discussions with his representatives this morning and we are waiting to hear back from them.
"We are in a good position. We don't want to sell. We feel we have a lot to look forward to in the second half of the season.
"We don't want any of our top players to go and Gary comes into that bracket."
Lennon added: "I've not spoken to him today because I was with his representatives most of the morning, so I'm sure they'll have a discussion about what was said between ourselves later on. He is preparing to start (on Saturday)."
- Sports & Recreation