David Beckham's craving for fame and celebrity led him to believe he was bigger than Sir Alex Ferguson and left the club with no option but to sell him to Real Madrid, according to the former Manchester United manager.
Beckham enjoyed 10 trophy-laden years at Old Trafford under the Scot's tutelage but his relationship with Ferguson deteriorated significantly towards the end of his time with the Premier League giant, and culminated in the infamous boot throwing incident that followed an FA Cup defeat at the hands of Arsenal.
In his new book Alex Ferguson: My Autobiography the 71-year-old reveals that it became obvious Beckham had allowed himself to be distracted during his final season at Old Trafford and led to the sort of mistakes which triggered one of the biggest bust-ups in Ferguson's 26-year reign.
"The confrontation between us that caused so much excitement around the game was an FA Cup fifth-round tie against Arsenal at Old Trafford in February 2003, which we lost 2-0," he said.
"David's offence in that particular game was that he neglected to track back for the second Arsenal goal, scored by Sylvain Wiltord. He merely jogged. At the end I got on to him. As usual, with David at that time, he was dismissive of my criticism.
"He was around 12 feet from me. Between us on the floor lay a row of boots. David swore. I moved towards him, and as I approached I kicked a boot. It hit him right above the eye. Of course he rose to have a go at me and the players stopped him. 'Sit down,' I said. 'You've let your team down. You can argue as much as you like.'
"I called him in the next day to go through the video and he still would not accept his mistake. As he sat listening to me, he didn't say a word. Not a word.
"'Do you understand what we're talking about, why we got on to you?' I asked. He didn't even answer me.
"The next day the story was in the press. In public an Alice band highlighted the damage inflicted by the boot. It was in those days that I told the board David had to go."
Rather than any errors on the pitch, however, it was Beckham's audacity in challenging his manager's authority that led him being sold to Real Madrid in the summer of 2003 for 23 million pounds.
Ferguson added: "David was the only player I managed who chose to be famous, who made it his mission to be known outside the game. In his final season with us, we were aware that David's work-rate was dropping and we had heard rumours of a flirtation between Real Madrid and David's camp.
"I used to say, 'The moment the manager loses his authority, you don't have a club. The players will be running it, and then you're in trouble.'
"David thought he was bigger than Alex Ferguson. There is no doubt about that in my mind. It doesn't matter whether it's Alex Ferguson or Pete the Plumber.
"The name of the manager is irrelevant. The authority is what counts. You cannot have a player taking over the dressing room. Many tried. The focus of authority at Manchester United is the manager's office. That was the death knell for him."