The 22-year-old joined the Red Devils in a £17million deal from Atletico Madrid in the summer of 2011.
He struggled for form in his first season at Old Trafford, making a few early high-profile errors and sharing goalkeeping duties with Anders Lindegaard.
However, De Gea appears to have found more consistency in his second season with the club, helping them build up a 15-point lead at the top of the Premier League.
His displays have been rewarded with a call-up to the Spain squad for World Cup qualifiers against Finland and France next week.
The Madrid-born star believes he has benefited from his time in England, both on and off the pitch.
"It's my second season in England and it has changed me both as a person and a footballer," he said.
Speaking of his Spain call-up, De Gea told AS: "I am very pleased and happy. This is a special moment for me and a big step in my career. I will try to do my best to impress the boss.
"It's a pity Iker Casillas is out. We all know he is our captain and a legend but I'm happy to be here, even if it's because of his injury."