Ex-Celtic forward Harald Brattbakk says the club would be forced to sell Odsonne Edouard if a £40m offer arrived.
"I think it would be really tough to say no to a bid of that amount. It's so much money," Brattbank told the Daily Mail.
"Financially, Celtic is still doing well. But any club would appreciate £40m right now. Also, if you sell him for that kind of money, you could buy one or two new players for maybe £10m and you'd still be left with £30m.
"This is always the discussion that you have. The club will always think about 10-in-a-row but also about how best to run it.
"If you ask the supporters, of course, they'd all give Édouard a better contract to stay on. But it's not that easy. The board of directors have to think about both things which makes it difficult."