Van Nistelrooy, 30, ended his five-year stint at Old Trafford by sealing a 10.2-million-pound (15m euro) transfer to Madrid last week, a move which has led to rare criticism of Ferguson from the United supporters.

Having scored 150 goals in just over 200 games for United, van Nistelrooy has proven to be a prolific goalscorer for the club since his 19-million-pound arrival from PSV Eindhoven in 2001.

However, having been dropped in favour of French striker Louis Saha for the League Cup Final against Wigan last February, Ferguson claimed that Van Nistelrooy's response to losing his place was not conducive to him remaining at United.

Ferguson said: "The difficult thing with footballers of today is the satisfaction that you have to give to them and part of that is picking the team.

"When Europe decided to bring in larger squads for players in their competitions, it became the most difficult thing for a manager because when you had to pick for a major game, there were always two or three players you were hesitant to tell that they were out.

"That was because they were great players, had been great players for you in the past and you had been with them a long time and formed a certain relationship with them.

"You just hope that they wouldn't argue against the manager's reasons for leaving them out.

"Sometimes they are not happy and I don't have a problem with that, but it is how they adapt that's important and Ruud was different in that way. That is exactly what happened."

Although Ferguson has yet to replace Van Nistelrooy by attracting a new striker to Old Trafford, the midfield area at the club has already been bolstered by the 18.6-million-pound arrival of England player Michael Carrick from Tottenham.

Carrick is set to make his United debut against FC Porto in the Amsterdam Tournament here on Friday evening and the 25-year-old is likely to be joined at Old Trafford early next week by the Villarreal midfielder Marcos Senna. United are close to agreeing a four million pound deal for the Brazil-born Spain international.

Ferguson said: "We are looking at other players and I think something will happen next week. There is an interest in Senna, there is an interest in others as well.

"We are trying to find different combinations in midfield. Carrick gives us one and the player who will possibly come in next week will give us another option.

"Over the time I have been at the club, we have had to build four or five teams. It's not always easy, but this team we are trying to build will hopefully stay together for a few years."