The striker is a target for Norwich City and Tottenham.
Lennon said: "I'd say there would maybe be one or two players wanting to leave at the end of the season and sometimes it's impossible to prevent that.
"But I wouldn't necessarily say Gary would come into that bracket.
"We had a chat with his representatives on Wednesday.
"It's not fair to assume negotiations over his contract won't go any further.
"We are still working on the contract. There are no guarantees on anything."