QPR are reported to have offered £4.5 million for the former Scunthorpe forward, who has been the subject of failed bids from Norwich and Hull this year.
Manager Neil Lennon previously revealed Hooper had probably played his last game for the Glasgow club and the forward, who has been struggling with a groin strain, was absent as the Celtic squad flew to Belfast for their Champions League qualifier against Cliftonville.
"A bid came in last night," Mjallby said at Glasgow Airport. "I don't know how the club has responded to it.
"They increased the bid a wee bit when it came in yesterday. If it is good enough, I don't know. That's something you have to ask the chief executive, the manager and the board.
"We know it looks likely right now that Gary is going to leave the club. I'm not too sure the final word has been said yet. We have to wait and see.
"I think the club is going to sit down and think about it. If he has played his last game, I don't know."
Celtic have a number of players injured for the second qualifying round first leg with Joe Ledley, Adam Matthews, Virgil van Dijk and Charlie Mulgrew all out.
Nigeria defender Efe Ambrose is unavailable after being given extra time off following the Confederations Cup, but Scott Brown has been training after recovering from a groin injury.
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