De Gea was heavily scrutinised during his debut season with United, having arrived from Atletico Madrid as a £17.8 million replacement for Edwin van der Sar in 2011.
The Spaniard's physique and decision making were brought into question, while a dip in form saw him axed by Alex Ferguson in favour of understudy Anders Lindegaard.
De Gea - winner of United's Player of the Year award last term - has gone on to silence his critics and in a big way after singlehandedly denying Everton victory in a man-of-the-match display on Sunday.
The 23-year-old stopped a first-half penalty before producing a stunning save to flick the ball over the crossbar in the final minute of injury time as United won 2-1.
Looking back at his early struggles, De Gea conceded he was forced to think about a return to Spain, but feels he is better for the experience.
"Sometimes it was difficult when you get a lot of criticism like I did," said De Gea, whose form was rewarded with his first Spain cap in June.
"But I kept strong and I always tried to remain positive. I loved training. It was a great pleasure, so I just did my work and worked through it.
"Those early days were difficult for me and my family. But when you play for a big club like Manchester United it is normal when you don’t play well.
"Yes I am glad it happened in some ways because the criticism makes you stronger. A goalkeeper is a difficult position and you make mistakes. It is normal.
"But you have to be strong in your mind to get through it all and get better."
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