The on-loan defender has made 42 appearances for the Championship club this season but, after he picked up two suspensions in less than a month, Warnock has decided to release the Celtic man.
The Leeds boss told the club's official website: "I have decided we won't be signing him for next season. I've had a chat with him, and I'm going to let him have a break before he goes and plays in the European Championships in the summer."
Warnock added: "We thank him for what he's done but I do feel it's time to move on in that area. He's had good games and average ones, but one or two people have come into my reckoning now that I'm looking for, and hopefully we can tie those players up now over the next few months."
Warnock also revealed that striker Billy Paynter will not feature again this term.
He said: "Billy will miss the rest of the season. His Achilles is very sore, and I think we just have to confirm it."