Sir Alex Ferguson has admitted 'one or two' of his players may be getting too old.
Manchester United have signed midfielders Owen Hargreaves, 26, and Anderson, 19, as well as winger Nani, 20.
"It's never easy breaking up a team, but you have to look at the long term," he told the News of the World.
"When you're at a club for 20 years, it's impossible to keep the same team. You have to face the horrible prospect that one or two of your players are going to get too old.
"I've had this with several players over the years."
However, he knows it could take time for Anderson and Nani to adapt and mature, and says he is building a side for the future.
"Putting the current team together has been a process of rebuilding. When we signed Cristiano Ronaldo and Wayne Rooney, we were thinking about the future, not just the present.
"There are times when you have to take the hit and be patient when it comes to the younger lads.
"It doesn't always come off and occasionally you have to wait, because they don't have the consistency, but what you hope they do is bring you hope and a dream.
"I'm confident now."
