Revealed: Van Nistelrooy left United because of a dispute with Ronaldo
Here is what Campbell had to say on the matter (via SI.com): " He told Cristiano that he had found a new father in Carlos Queiroz (Ferguson's assistant manager at the time) a little after Cristiano's real father had died of alcoholism. Carlos told him to have some respect but he said that he didn't have to respect anybody. He then later excused himself but Cristiano did not accept it. Ferguson sent Van Nistelrooy home when he heard what happened and he was then moved to Real not long after that. Ruud always put himself first which was a problem indeed...".