The 32-year-old is expected to join City in the January transfer window.
“We have had approaches for Shay – serious approaches from Man City,” he said in The Daily Telegraph.
“Irrespective of all the stories, they’ve offered £5 million and not a penny more.
“We think it’s an insult to offer that for the best keeper in The Premier League. It’s a derisory offer, but Shay has made it clear he wants to leave.
“I wasn’t involved too much with the meeting between the owner, Shay and his agent when they tried to thrash it out.
“But as far as I know, the owner and the managing director were unhappy they’ve only been offered £5 million.
“That’s where we stand. I don’t want to lose him – I’m fighting a relegation battle.”