In his new book, Ferguson described his former midfield talisman as an 'intimidating, ferocious individual' and claimed he had 'the most savage tongue you can imagine. He can debilitate the most confident person in the world in seconds.'
Keane left United in November 2005, just a few weeks after incurring the wrath of his manager for criticising team-mates in an interview for MUTV.
"I'm OK, quite relaxed," Keane told ITV Sport. "I remember having conversations about loyalty when I was at the club and I don't think he knows the meaning of the word.
"To constantly criticise other players that brought him success ... I 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.
"A lot of these players helped win a lot of trophies. It's just part of modern life. People like to do books and criticise ex-players."
Check out our at-a-glance guide to Sir Alex Ferguson's autobiography which was launched on Tuesday.
Ferguson reveals he turned down the opportunity to manage England on two separate occasions. Firstly, he says he was approached in 1999 just before Kevin Keegan took the job and then two years later prior to the appointment of Sven-Goran Eriksson. Ferguson said: "There was no way I could contemplate that. It wasn't a bed of nails I was ever tempted to lie on."
Keane and Ferguson's relationship soured in 2005 when the United captain became angry at Ferguson over conditions at the club's pre-season training camp. Ferguson says he decided to sell Keane after that incident. Then came an interview with MUTV in which he "slaughtered" a host of United players. In a team meeting afterwards Keane accused Ferguson of bringing his personal affairs in to the club over the Rock of Gibraltar case. Recalling Keane's mood at the time, Ferguson said: "It was frightening to watch." Keane was sold to Celtic, but turned up at the United training ground to apologise to Ferguson later that season, the Scot says.
Ferguson does not go in to too much detail about Rooney's supposed transfer request last summer - only that the striker was annoyed at not playing often. He does reveal more about Rooney's plea to leave in 2010, when the former Everton man told Ferguson that the club were not ambitious enough. Rooney said Ferguson should have signed Mesut Ozil, now at Arsenal.
Ferguson enjoyed many a tussle with United's bitter rivals. He said he found former manager Graeme Souness to be a "good guy but impetuous". Ferguson says Rafael Benitez was a "control freak" and branded the Spaniard's famous "facts" press conference "silly". "The mistake he made was to turn our rivalry personal," Ferguson says. Ferguson is also critical of Kenny Dalglish's £20million signing of Stewart Downing in the book.
Sheikh Mansour's purchase of United's neighbours in 2008 gave Ferguson a new, rich rival. Ferguson describes losing the title to City in 2012 as the worst day of his life. Ferguson criticises then manager Roberto Mancini in the book over his failure to sell former United striker Carlos Tevez when he reportedly refused to come off the bench against Bayern Munich. "In terms of his prestige as a manager, he let himself down," Ferguson says.
Ferguson says Beckham's football was affected by his celebrity lifestyle. He said the midfielder's workrate dropped in his final year at the club. After an FA Cup defeat to Arsenal in 2003, Beckham's eyebrow was cut after a row in the dressing room between Ferguson and his star midfielder. "David swore. I moved towards him, and as I approached I kicked a boot. It hit him right above the eye," Ferguson says.
Ferguson claims his once-fiery relationship with the Arsenal manager mellowed by the end of his time in management. One flashpoint during their rivalry came in October 2004 when United ended Arsenal's 49-match unbeaten run. Ferguson was left covered in pizza following a furious row between staff and players from United and Arsenal. The row came after Ruud van Nistelrooy claimed Wenger berated him as he left the pitch. Ferguson says he does not know who threw the pizza, but claims Wenger's "fists were clenched" when the Scot confronted him over Van Nistelrooy's claims.
RUUD VAN NISTELROOY
Van Nistelrooy was one of the best goal scorer's of Ferguson's reign, but the Scot claims the striker asked to leave just three days before the FA Cup final of 2005. He stayed, but after a training ground bust-up with Cristiano Ronaldo, Ferguson said he had no choice but to sell the Dutchman, who has since apologised to his former boss.
Ferguson criticises the anti-doping testers who turned up to take a urine sample from Rio Ferdinand in September 2003. Ferdinand missed the drug test and Ferguson blames the testers, who he claims were sat around having cups of tea, rather than going to the training field to wait for the defender to come off the pitch. Ferdinand received an eight-month ban, which Ferguson is critical of in the book.
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