The 24-year-old, who still has 18 months left on his contract, has been linked with a move to Norwich in recent weeks.
"There's a bid, but it's very disappointing it has been made public knowledge," Lennon told Sky Sports News.
"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."
Hooper has scored 17 goals in 29 appearances for Celtic this season.