Villa face United in the Carling Cup final on Sunday and Warnock is backing Villa centre-backs James Collins and Richard Dunne to stop Rooney.
“Richard and James have got a tough task ahead of them – but Rooney will find it tough to do much against those two as well,” Warnock told Sky Sports.
“They are two of the best defenders in the league on form and have been fantastic all season.”
“Rooney is one of those players I love watching on TV,” he added.
“You would put him, Messi and Ronaldo in the same bracket as the three best in the world.
“You could argue all night about who is the best out of those three but he is one of those players you want to watch which is something that can’t be said about every player.
“He has got all the ability in the world. I’ve been lucky to train with him (with England) and realise how good he is and it is even better when you train with him. You realise what he can do.”