Ferguson dropped Van Nistelrooy for the Carling Cup final

Striker Van Nistelrooy joined Real Madrid in a �10.3m deal on 28 July.

Ferguson said no player was happy to be dropped, but added that their reaction to not being picked was important.

"How they adapt to it is different with every player. Ruud was different in that way. That is exactly what happened," said Ferguson.

Despite scoring 150 goals in five-year spell at Old Trafford, Van Nistelrooy found himself out of favour towards the end of last season.

He was replaced by Louis Saha for the 4-0 win over Wigan in the Carling Cup final at the Millennium Stadium.

After joining Madrid, Van Nistelrooy said the breakdown of his relationship with Ferguson was the only reason he wanted to leave.

But Ferguson said the modern game involved big squads which meant that even established players were at risk of being dropped.

"It makes it difficult for a manager because every time you come to pick a team for a major game there are two or three players you are hesitant about telling they are out of the team," he said.

"That's either because they are great players, they have been great players in the past or you have a certain relationship with them."

"All you can do is hope they will agree with the reasoning behind your decision.

"Of course, sometimes a player doesn't agree. I am happy with that."

At the time, Ferguson claimed Saha deserved his place because he had played in most of the earlier rounds.