In his new self-titled autobiography, Sir Alex Ferguson is critical of David Beckham for his desire for fame and for thinking he was "bigger than the manager."
Beckham and Ferguson won six Premier League championships, two FA Cups and one Champions League title at Manchester United before the superstar was sold to Real Madrid in 2003. Beckham later signed to play Major League Soccer for LA Galaxy.
Ferguson said the former England captain had to leave United because of his ego. Ferguson and Beckham had a falling out after the manager was critical of Beckham's performance during an FA Cup defeat by Arsenal in 2003.
"The minute a Manchester United player thought he was bigger than the manager, he had to go," he wrote. "David thought he was bigger than Alex Ferguson.
"That was the death knell for him."
In the book, Ferguson describes his version of the dressing-room incident with Beckham that followed the FA Cup loss to Arsenal and his call for the star's transfer.
"He was around 12 feet from me," wrote Ferguson. "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.'
"It was in those days that I told the board David had to go."
Ferguson believed Beckham's celebrity lifestyle affected his play following the player's marriage to pop star Victoria Adams.
"David was the only player I managed who chose to be famous, who made it his mission to be known outside the game."
In a press conference on Tuesday to launch his book, Ferguson added: "He fell in love with Victoria - that changed everything."