According to The Independent, the "incidents in training" that Ferguson referred to were manifestations of the rapidly-deteriorating relationship between Van Nistelrooy and Cristiano Ronaldo.
Ronaldo has been the subject of Van Nistelrooy's ire on a number of occasions, with the Dutchman critical of his Portuguese team-mate's tendency to hold onto the ball for too long - a trait Van Nistelrooy felt was costing both United and himself vital goals.
A training ground bust-up between the two in January ended with punches being thrown, and a second incident on Saturday morning reignited the ill-feeling between the two players.
During 'a heated exchange' Van Nistelrooy told the young Portuguese to go and talk to "his dad" - a disparaging reference, says The Independent, to United assistant manager Carlos Queiroz.
The remark carried particular sting, as Ronaldo lost his father in September - a bereavement that has been widely seen as responsible for the very loss of form earlier in the season that Van Nistelrooy was so critical of. A 'clearly upset' Ronaldo replied that he 'did not have a dad'.
Van Nistelrooy then arrived on Sunday having thought no more of the incident - only to be told that he was not included in the match-day squad. On hearing that, the Dutchman said to club captain Gary Neville: "Good luck for the game. I'm off."
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