It's believed the bid is around £4.5m for the former Scunthorpe forward, who has been the subject of failed offers from Norwich and Hull this year.
Mjallby said: "A bid came in last night - I don't know how the club has responded to it.“If he has played his last game, I don't know”Johan Mjallby
"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 think the club is going to sit down and think about it. If he has played his last game, I don't know."
Manager Neil Lennon previously revealed Hooper had probably played his last game for the Hoops.
The striker, who has been struggling with a groin strain, was absent as the Celtic squad flew to Belfast this morning for their Champions League qualifier against Cliftonville.
The R's are trying to fund the move by offloading Frenchman Loic Remy.