United were looking for a place in the FA Cup finals but lost in a resounding manner to Chelsea as a result of various errors from De Gea (1-3).
The goalkeeper returned to the fore after his dismal display and Ferdinand asked his ex-team for a change in goals.
"Who is out there right now that could be bought, that is able to be a world-class goalkeeper at Manchester United? The only one I see is Oblak but can you get him out of Atletico Madrid?", he started saying.
Likewise, the ex-United player also continued in the same line: "If you do, how much would you have to spend? An obscene amount of money".
But Ferdinand, who admitted feeling "disappointed with De Gea", understands that Oblak is out of reach because of financial issues. "I say, stick with him. He's earned the right to be stuck with", he noted.
Meanwhile, Chelsea, the Red Devils' executioner in the FA Cup semi-finals, are considering moving on from the Slovenian goalkeeper.