The Republic of Ireland full-back was bought from Oldham Athletic in 1990 for just over £600,000 and during his 12 years at the club he racked up seven league titles, three FA Cups, one League Cup, one European Cup and one Cup Winners' Cup.
"People ask you who is your best Man United team," said the former Old Trafford boss at a question and answer evening in Glasgow to coincide with the publication of his autobiography.
"It is absolutely impossible. You look at the strikers I had, going back to (Brian) McClair, (Mark) Hughes, (Andy) Cole, (Eric) Cantona, (Ruud) van Nistelrooy, (Louis) Saha, Ole Gunnar Solksjaer, (Dwight) Yorke, Teddy Sheringham.
"Then to the present players, Wayne Rooney, (Robin) van Persie, Chicharito (Xavier Hernandez).
"How do you pick out of that? Cantona and somebody else?
"The midfield was probably a bit easier because you have (Roy) Keane, (Bryan) Robson and (Paul) Scholes, they were fantastic players and (David) Beckham, (Cristiano) Ronaldo and (Ryan) Giggs.
"But honestly, I would say Denis Irwin would be the one certainty to get in the team. I called him an eight out of 10.
"At Highbury in one game he had a bad pass back in the last minute and (Dennis) Bergkamp came in and scored.
"After the game the press said 'you must be disappointed in that pass back.'
"I said, 'well, one mistake in 10 years isn't bad.' He was an unbelievable player."
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