Doyle, 27, is one of the longest-serving players at St Andrews as this is his 12th season there and he made his debut in 2006: "It's nearly half my life as I'm 27," he says.
But he's been back-up keeper for most of that time and has made just seven league appearances in the last two seasons.
The Cork native has stood in for Butland in Cup games this season and boss Clark is happy with Doyle's form and has promised not to sign another keeper if the cash-strapped club decide to sell Butland, who has been linked with Premier League clubs including Chelsea.
"If Jack goes there will not be a replacement goalkeeper coming in. Colin will be the No.1," said Clark. "I think he has been excellent for us, he's played the cup games and if in the next two weeks something does happen with Jack, Colin has had a couple of games and he's not going straight through and into the league programme on the back of not playing."