The former midfielder believes the Scot is out of line for criticising several former players, including David Beckham, Ruud van Nistelrooy and Wayne Rooney, in his new book
Ferguson had stated that Keane went past the point of no return when he severly criticised his team-mates in an interview with United's in-house television channel in 2005.
Before being locked away, the interview was shown to the United squad, prompting a mass row, and Keane was duly sold to Celtic - a move Ferguson says helped the team relax.
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"I do remember having conversations with the manager when I was at the club about loyalty," he told ITV Sport. "In my opinion I don't think he knows the meaning of the word.
"It doesn't bother me too much what he has to say about me but to constantly criticise other players at the club who brought him a lot of success I find very, very strange.
"But I certainly won't be losing any sleep over it. I just don't think the manager needs to do it. I don't know how many books he's written now but you have to draw the line eventually, to say listen these players have all been top servants to Man United and a lot of these players helped the manager win lots of trophies so
"Can you imagine if we never won a trophy what he would have said? We brought success to the club, we gave it everything we had when we were there so; but as I said it's just part of modern life now. People like to do books and criticise their ex-players."