United and Middlesbrough will face off in the FA Cup fourth-round.
"They've got great individuals but not a team and I don't see that coming," Warnock told talkSPORT.
"They've got my old team, Middlesbrough, in the next round of the FA Cup and I wouldn't swap any of their defenders for the back-three at Middlesbrough – Dael Fry, Anfernee Dijksteel and Paddy McNair.
"I think they're better than Man United's defence."
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