The 24-year-old striker has been the subject of continued media speculation over his future in recent months.
Hooper, who still has 18 months on his contract, has previously stated his desire to remain at Celtic Park.
Lennon refused to discuss details of the offer but admitted to being bemused the matter had been made public with Celtic continuing to talk with the player's agent over a new deal.
"There's a bid," he said. "But it's very disappointing it has been made public knowledge.
"We do our business as privately as possible and it's been leaked out somewhere, so I'm not happy about that.
"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.
"And that's always been the case. We don't want any of our top players going, and Gary comes into that bracket."
Norwich could now be tempted to raise their offer for Hooper, who Canaries boss Chris Hughton has watched several times in recent weeks.
Hughton, however, remains coy about how much business he might do in the January transfer window.
"It is our duty if we're able to improve the squad, but I have no real interest in anybody leaving," said Hughton, who denied knowledge of any move by Wolves for Canadian striker Simeon Jackson.
"Numbers-wise we're fine as regards the squad. The injury situation hit us a bit up front having Grant Holt and Steve Morison out for a period of time.
"Can we add to it? If we are able to add some quality to what we've got we'd gladly do that. We are ambitious here. We do want to develop but it has to be in the framework of the club."