Spain international De Gea finally put pen to paper on a new long-term deal at Old Trafford last week, committing his future to the Premier League club until at least 2023.
The 28-year-old, an integral member of Uniteds team since joining in 2011, had been linked with Real Madrid, Barcelona and PSG over the last few years.
Mourinho says De Gea is a hugely talented goalkeeper but says he got lucky with his new deal worth £250,000-a-week after tax.
He told Sky Sports: I think the moment he signed his huge contract is a moment that I dont think Manchester United need to pay as much as they have.
One or two years ago the world was after him. At the moment, the majority of the big doors are closed. Real Madrid are closed. Barcelona are closed. PSG are closed.
I dont think United were under pressure because David was going to disappear. So he gets a phenomenal contract in a moment when hes a bit lucky to get it.
Is he good? Yes, hes very good. But just like [Manchester Untied defender Victor] Lindelof, he is better at some things than others.
David is much better on the line than he is coming out. In goal, his technical level is good.
Despite developing into one of the most highly-rated goalkeepers in the world, De Gea has made a number of high-profile errors over the last 18 months.
But the Spaniard hit back at his critics after signing his new contract, telling Sky Sports: I think people, when they look back on last season, they are thinking about the last few months.
If you focus on the season as a whole and, in particular, the first seven months of that season I was quite happy with my form.
You can say the contract is there in the background – its not even in the back of yRead More – Source