Keane takes aim at the Scot, who lifted the lid on his differences with Keane and David Beckham among others in his autobiography last year, in his updated memoir The Second Half.
The 43-year-old, who accuses Ferguson of being "childish" in his dealings with him towards the end of his illustrious Old Trafford career, was pulling no punches at the official launch of his book in Dublin on Thursday afternoon.
Asked if he would ever forgive the former United boss, Keane said after a pause: "Good question. I'm not sure, I'm not sure.
"Football is a small world and eventually, you will cross paths with people again. Whether I would ever bump into him or not, whether it be at a game or sometimes there are conferences going on...
"The problem, I suppose, I had and one of the reasons when you are writing stuff and you are reflecting on it, is that when you have worked with somebody for such a long time - and obviously we had our disagreements and I departed, and I have no problems with that, it's fine - it's afterwards when people start coming out with all sorts of nonsense.
"For Alex Ferguson, not just to criticise myself, but other players who were part of a team that brought some good days to lots of supporters, for him to criticise that when you think of what he made out of it - he made millions of pounds out of it...
"He got his statues, he's got his stand named after him - to come back and criticise...
"I said at the time, I wasn't too bothered about myself, but to criticise people who brought him success was just ridiculous.
"Will I ever forgive him? I don't know. Listen, I don't know. We'll see if we ever cross paths again. I'm sure we will - cross paths, I mean."
Keane uses the book, in which he takes aim at a variety of targets including Ferguson and old foe Alf-Inge Haaland, and explains his decision to reject Celtic's approach to become their manager during the summer, to set the record straight.
He was mentioning no specific names, but was keen to hit back at what he described at the "lies and lies and lies" he believes have been told about him.
Keane said: "The stuff that has been said about me over the years, even from ex-team-mates, is a pack of lies, just lies and lies and lies, and sometimes you just say, 'Listen, I have got to get up and say something myself and defend myself a little bit', and hopefully the book will reflect that."
However, while the book, which was written in conjunction with Irish author Roddy Doyle, allowed Keane to get certain things off his chest, he insists it is not all negative, and, although former Nottingham Forest manager Brian Clough is treated more favourably than Ferguson, he credits much of his success as a player to the men he played alongside.
He said: "People are always quick to praise coaches and managers, and I've done that with Brian Clough, but the people who helped me the most from a football point of view were my team-mates. It is as simple as that.
"I've never worked with a coach or a manager where they inspired me to do something. The people I learned the most from were the people around me - Stuart Pearce, Steve Bruce, Gary Pallister. These boys, when you go into battled with them...
"I think managers today get too much credit - and also on the other side, they get too much criticism when things go wrong."
Keane is currently combining his duties as Aston Villa's assistant manager with a similar role under Re[public of Ireland boss Martin O'Neill, and, while a return to club management interests him, he insists he is not sitting by the phone waiting.
He said: "I'm not waiting for a manager to lose his job - I'm not that type of personality. I hope managers do well. But obviously the game doesn't work like that - managers will lose their jobs.
"But I'm not sitting around waiting for the phone to ring, I have to say."
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