De Gea, who joined United for a reported £18.9million last year, was dropped after the opening two Barclays Premier League games of the season.
The Spaniard has returned in the Champions League and Capital One Cup but has lost his number one status with Anders Lindegaard taking over for the last four league matches.
Ferguson must now decide whether to retain De Gea, 21, after he played at Cluj on Tuesday or switch back to Dane Lindegaard, 28, for Sunday's Barclays Premier League trip to Newcastle.
Ferguson said: "He (De Gea) was excellent, he is an outstanding goalkeeper, the young lad, he is getting better all the time.
"I don't know whether I should play him on Sunday or not but the way we have been doing it in the last few weeks has worked quite well for us.
"Everybody wants to play, goalkeepers are no different, but the way I look at it at the moment is getting the two of them experience will help me in the long term.
"Obviously at some stage one of them will take over if he shows a real consistency in top-level performance and he has shown a maturity.
"At the moment neither of them have got that big-game experience. They will get that in time."
Ferguson seems at ease with the fact he currently does not have a first-choice goalkeeper and he feels both players have plenty of time to establish themselves.
Former United goalkeeper Edwin van der Sar was 40 when he retired in 2011 and Ferguson has pointed to other examples of players enjoying long careers.
He said: "Peter Schmeichel was 27 when he joined us. Everyone was talking about a young goalkeeper joining us but he was 27, and he gave us eight great years.
"Goalkeepers can play until their late 30s quite easily, look at Brad Friedel for instance, and Peter Shilton played in the 1990 World Cup and I think he was 40.
"Goalkeepers can last longer. If they look after themselves even better, but as long as they keep their agility and their speed they can play to a good age."