An £18million summer signing from Atletico Madrid, De Gea endured a difficult start to life in England but seemed to have put his problems behind him in recent weeks.
However, they resurfaced on New Year's Eve when the 21-year-old was responsible for Blackburn's shock winner at Old Trafford.
That triggered the return of Anders Lindegaard, who had kept clean sheets in the previous two games, for the trip to Newcastle, although it did not do United much good as they crashed to a 3-0 defeat.
However, the Denmark international was blameless for the opening two goals and it is widely expected he will keep his place for Sunday's FA Cup tie at Manchester City.
And despite the short-term issues, Ferguson is certain he got the right man when he chose De Gea to replace Edwin van der Sar.
"De Gea is the long-term prospect, there is no question about that," Ferguson said. "Anders has done very well. He has provided tremendous opposition to David. But the potential of David is obvious."
If Lindegaard does play on Sunday, it would be his fourth appearance in United's last five matches, but Ferguson does not view that as a permanent transition.
"We have been leaving him (De Gea) out of games quite regularly," he said. "There has been a nice mix of opportunities for Anders Lindegaard, playing in Europe and some of the league games.
"Just because he (De Gea) has lost two bad goals against Blackburn doesn't mean that all of a sudden we are neglecting that part of both of them playing."
Ferguson's team selection could be influenced by what players are available to City, specifically Yaya Toure.
On Thursday, Blues boss Roberto Mancini claimed Toure would not be able to play because he was required to attend a team meeting in Paris on Saturday before the Ivory Coast squad flew out for a two-week training camp in Abu Dhabi ahead of their African Nations Cup campaign.
However, the meeting was scrapped and training does not begin until Monday, which points to Toure and brother Kolo being available.
However, team-mate Cheik Tiote was not part of the Newcastle squad for their FA Cup tie with Blackburn on Saturday, so the Toure brothers could still be absent as well.
Ferguson will be without a few more than that though, and the United boss has confirmed it will be another month before either Tom Cleverley or Ashley Young can expect a return to match action.
Cleverley has played just twice since the beginning of September after suffering foot and ankle injuries, while Young sustained a knee injury at Fulham last month.
"The plan for Cleverley is to start running two weeks on Monday and join us the following week. He is maybe a month away," Ferguson said. "Ashley is four weeks away easily.
"The bleeding never came out after the Fulham game and is only starting to come out now. That has been unfortunate. We don't think it is a serious injury but we can't prejudge it until we have all the facts."
Little wonder that Paul Scholes has been hinting he would be willing to come out of retirement, which would be a more plausible move than signing Frank Lampard.
And while Ferguson does have plenty of striking options, it seems Michael Owen will not be among them for a while.
"When Michael gets an injury, it is always a bad one," Ferguson said of the ankle injury the former England international suffered against Otelul Galati in November. "Maybe the middle of February he should be back.
"That could be a good time for us. His ability to score goals out of nothing is always valuable."