The Irishman admits it was his "hobby" during his early Old Trafford career.
Asked by ShortList magazine if Ferguson ever had words over his drinking, Keane said: "Oh, of course. And quite rightly.
"This idea that me and Ferguson just had one bust up right at the end We had loads! We had disagreements about my drinking, as fans are happy to report you if you're spotted out at 3am.
"But if we had a game on a Wednesday and the manager said to me, 'I heard you were out Sunday night,' I'd say, 'Yeah, I go out Sundays.' I was single, I was 21. I wasn't a golfer.
"Drinking was my hobby, I suppose. I'm not giving it the thumbs up, but it was my trait. I don't know why - because I'm Irish, maybe, because I lived by myself. Boredom kicked in."
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