The England Under-21 international has been linked with Everton, Liverpool and Sunderland in recent weeks after becoming a regular fixture in Clark’s first-team.
Brendan Rodgers is reportedly keen to find a long-term replacement for Spain international Pepe Reina, while David Moyes has also admitted his interest.
Birmingham fended off interest during the summer, and Clark insisted the St Andrew’s outfit have raised their asking price for the young shot stopper.
“By the time the window opens he’ll have played 25 or so Championship games,” Clark said.
“We would be looking for an even more substantial figure than we were offered in the summer – even though I certainly don’t want it to come to that.”
Clark also revealed he is keen to keep Butland and build his Birmingham side around the promising, young goalkeeper.
“Ultimately, it’s down to the board,” he added.
“He’s the future and the type of player I’d rather build my team around.”
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