Beckham left in 2003 when Fergie ruled it was time to sell him and he joined Real Madrid.
Beckham and Ferguson have since made their peace but whenever he moves clubs it makes waves.
He said: "I couldn't have stayed at United, it wasn't an option.
"This next move will be about football. That has never been any different for me.
"People say some of the moves have been about money but my career has never been about money. I'm not money motivated."