Sir Alex Ferguson - who managed the former England star during his time at Manchester United from 1993 to 2003 - insists the 38-year-old player ''changed'' when he started dating the Spice Girl and ''made it his mission'' to become famous.
In an extract from his new book, 'Alex Ferguson: My Autobiography', he wrote: ''He lost the chance to become an absolute top-dog player ... he never attained the level of an absolute top player ... He started to make decisions that rendered it hard for him to develop into a really great footballer.
''That was the disappointment for me. There was no animosity between us, just disappointment, for me. Dejection. I would look at him and think, 'What are you doing, son?'
''David was the only player I managed who chose to be famous, who made it his mission to be known outside the game.''
Speaking at a press conference to promote his book, Ferguson added: ''The big problem for me ... he fell in love with Victoria and that changed everything.''
Ferguson also claims Beckham - who played for England 115 times and went on to star for Spanish giants Real Madrid after leaving Manchester United - thought he was ''bigger'' than him during his final few years at the club.
The 71-year-old Scot recalls one incident before a warm-up on a match day when Beckham refused to take his beanie hat off before going onto the pitch because he wanted to wait until kick-off to unveil his new haircut.
Ferguson claims Beckham ''went berserk'' when he insisted he remove his headgear.
He wrote: ''At that time I was starting to despair of him. I could see him being swallowed up by the media or publicity agents.
''The minute a Manchester United player thought he was bigger than the manager, he had to go.
''David thought he was bigger than Alex Ferguson ... that was the death knell for him.''
Ferguson also recalled an infamous incident in 2003 when he accidentally kicked a boot at Beckham's head in the dressing room when they were arguing after a game, which led to the hunk requiring stitches on an injury just above his eye.
He wrote: ''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.
''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.''
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