The Championship club have been attempting to strike a deal for Hooper, who is into the final year of his contract.
But Lennon has not completely given up hope of persuading him to stay, and last season's top scorer was named in the squad for the second leg of Celtic's Champions League qualifier against Cliftonville.
The manager said: "It's between Gary's representatives and the club in question but for the time being he's still a Celtic player.
"You never say never. If things aren't agreed, or things don't go through, he'll be here for at least another year anyway.
"I'm hoping to speak to him - I haven't had the chance in the past week or so.
"His mind may be elsewhere, this has been protracted now for a few weeks, but I'll just make it clear he's welcome here and we want him to stay."