The pair are now both successful managers, and Warnock claims McCarthy used to clean his boots when they were apprentices.
"He used to clean my boots when I was a kid," said Warnock, who will pit his wits against the man 10 years his junior at Molineux on Saturday.
"He denies it but he was an apprentice at Barnsley with me.
"He was a massive lad in those days. I've never seen anything like it.
"He was like a brick... you can't say that on the television, can you?
"But he was built very, very big and sturdy in those days."
Warnock admitted Wanderers were "18 months in front of" his QPR side, who won last year's npower Championship.
"They've had to go through a similar situation that we're going through," he said.
"Mick's moved on a level now and bought top players, I think, your (Kevin) Doyles and that.
"We're not anywhere near that level yet but that's where we want to be, where Wolves are, that next step up."