De Gea has made a series of errors for La Roja in recent months, the most high-profile of which came against Portugal in their World Cup opener as Cristiano Ronaldo's shot squeezed through his hands in Sochi.
Questions have now been asked in Spain as to whether he should retain his place for Wednesday's clash with Iran, with manager Fernando Hierro having been forced to defend his No.1 .
And ex-Red Devils stopper Bosnich believes the 27-year-old must now step up given fans have come to expect so much more since his arrival at Old Trafford.
"David de Gea is an excellent goalkeeper, he is one of the best goalkeepers in the world, but the other night he made a mistake that was a horrible mistake," Bosnich told Goal and Omnisport .
"That’s a goalkeeper’s nightmare. He rightly got criticism and he has got to come back from it now.
"Of course he is world class. That’s why the spotlight goes more on world class players and especially goalkeepers. When you do make a mistake, people don’t expect that. When it is a goalkeeper that no one has heard of before and he makes a mistake then they pretty much brush over it.
"When it is someone like David de Gea, when it is someone like Manuel Neuer or Thibaut Courtois, when they make mistakes people are going to turn around and say; 'Hang on a minute? What’s going on?'. It is only human nature."
Having drawn with Portugal in their opening game, Spain now must win in Kazan to maintain their chances of topping Group B.