Premier League club Norwich City have confirmed that they have made a bid for the 24-year old midfielder and despite Leeds offering him a new deal, Warnock feels he will be off for a crack in the top flight rather than sign a new Elland Road contract.
"Negotiations have been going on for weeks," Warnock told the club's official website.
"I was hoping he would have had a change of heart and I can honestly say that in all my time in football, I've never worked as hard in trying to keep a player.
"He was offered the best contract, the captaincy, and we would have built a team around him, so I am very disappointed.
"He's made it clear what he wants to do and he's had his head turned. He wants to play in the Premier League.
"He believes his Scotland international career may be better served in the Premier League, but I'm not so sure."