Hooper has entered the final year of his contract at Celtic Park, with Lennon under increasing pressure to make a decision over his top scorer.
Norwich City and Queens Park Rangers have both had summer offers rejected for the forward, but Lennon has conceded that Hooper may have played his last game for Celtic.
He is quoted by Sky Sports News as saying: "It will be difficult to convince Gary to stay.
"He has not featured much in pre-season and the games start in earnest for us on Wednesday night. So he'd have a bit of catching up to do and I don't know where his mind is at the minute.
"Has he played his last game for Celtic? Never say never but it's looking more and more that way."
The 25-year-old missed last night's 3-0 friendly defeat to Union Berlin after suffering a groin problem, with a return in time for Wednesday's Champions League qualifier against Cliftonville unlikely.