Warnock says he was offered the Scot when in charge of Cardiff City.
He told talkSPORT: "I think they had been tempted to let him go two or three times.
“I had his agent on a while ago saying 'I think he'll be leaving the club' but what's he done? He's done it on the pitch. He's worked his socks off, scored important goals and been part of that dressing room.
“They've got a great chance of getting in Europe. An absolutely great chance."