Former Manchester United mainstay believes Derby County and Nottingham Forest boss was superior to the legendary Old Trafford figure.
Roy Keane's new book release, The Second Half, has given way to a multitude of eye-opening one-liners and anecdotes.
In the biographical account, Keane - a seven-time Premier League winner and Champions League titlist with Manchester United - has claimed that he was coached by two all-time great managers during his playing days.
One, of course, was Sir Alex Ferguson who enjoyed an illustrious 26-year tenure at Old Trafford - and famously clashed with the tough-tackling Irishman.
Keane once told Ferguson that "we need more from you. We need a bit more, gaffer [as we're] slipping behind other teams."
At the end of his career with United, Keane claimed he felt like the club were preparing "hand grenades" to throw at him.
But regardless of the ups and downs with Manchester United, Ferguson was one of two coaches he rated the highest.
The only man he rated higher was Brian Clough, his mentor at Nottingham Forest between 1990 and 1993.
"I worked under two great managers and I put Brian Clough ahead of Alex Ferguson," he said.