The cash-strapped Championship outfit have revealed that they are willing to listen to offers for the England international in order to bring in finances to the club.
"The only official bid the club have had is the one that was turned down in the summer from Southampton, just as I was taking the job," said Clark. "That's not to say we haven't had lots of interest in Jack and people asking the question.
"But in terms of somebody actually putting down that they want to take him and what they're willing to pay, that hasn't materialised.
"With my football manager's head on, I don't want that to happen. But in terms of the future of the club, it's been talked about already by the chairman that it probably needs to happen."
Butland was ever-present for Team GB during the London Olympics last year.