The striker is in his third season since signing from Northampton Town and his manager is desperate for the transfer window to close before well-funded Championship clubs in England start sniffing.
Given that his scoring prowess is matched by a healthy work ethic, Butcher describes the player as "priceless".
"It is a concern [that we could lose him] and we have had to looked at that possibility, so we are ready and aware if something happens," said Butcher. "We have a Plan B and a Plan C in place but we don't want to operate those. We want Billy to be here and I have every confidence he will be."