He was speaking at a question and answer session for a 1,700-strong audience at The Lowry Theatre in Manchester to coincide with the publication of his autobiography.
However, he accepted it was because of the Anfield side's historic success that the rivalry between the two north west clubs was so fierce.
"Coming to United Liverpool were the top dogs, there were fantastic teams in the '70s and '80s winning their four European Cups - or whatever it was," he said.
"Our younger fans who have grown up don't remember when Liverpool were successful.
"They don't remember when we were fighting to get on top of Liverpool.
"The two clubs are the two most successful in Britain, that is obvious, so the rivalry is always going to be there."
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