The Red Devils have already snapped up Mexico striker Javier Hernandez and Fulham defender Chris Smalling for next season and Ferguson does not expect to be very busy in the market this summer.
Talking at the beginning of United's tour of North America Ferguson said: "In the market today it's very, very difficult and the structure of our squad is good in terms of ages, the balance, the numbers and there's a lot of good young players.
"Sometimes you have to trust in all the development of the last few years and I'm going to stick with that, or most of it.
"There may be one signing and maybe we'd like to get a good player to the club, of course, but it's not easy in the present day climate.
"I've nothing definite to tell you because we're still assessing whoever's available and the difficulties in terms of who you'd bring in."
United chief executive David Gill added: "Hernandez and Smalling are signings we've already made and the other point to bear in mind is that the Premier League is bringing in squad limits next year of 25, which we clearly operate in European competitions, but is now coming to the Premier League.
"There will be unlimited under-21s and other rules and we'll be taking all that into consideration."