Neville, speaking on Monday Night Football, had previously been critical of De Gea on the show during his first season at the club but only praised how good he is now but the rapid improvement in other areas of his game since he arrived at Old Trafford in 2011.
“We are now seeing a huge improvement in his game,” Neville said.
“He has always been a great shot stopper, he has been like that from day one.
“However, there are four other areas where he has greatly improved his game, the first being dealing with crosses, which I still think is his main challenge.
“This season there is a massive improvement on his intent. He is now catching and dominating. Incredibly, he has made just one punch, against Arsenal, all season.
“But if you look at the improvements he has made from where he was three years ago, it is absolutely staggering.
“On Sunday he was in control, dominating, standing up, making it difficult for Raheem Sterling and there is a massive improvement in that aspect of his game.”
Neville also praised De Gea for his ability to stop the majority of one-on-ones.
He added: “The ‘keeper has a similar style to former United star Peter Schmeichel in which he makes himself as large as possible and can regularly be seen making saves with a leg stuck out as he did from Mario Balotelli and Sterling on Sunday.
“I think a goalkeeper should save seven or eight out of ten one-on-ones.
“And this, for me, now is De Gea’s biggest change, he is dominating the one-on-ones, saying: ‘You beat me, I am not going to make your mind up for you.’ And he is winning United match after match, which is what I expect from a United goalkeeper.”
“There has been a physical maturity since two years ago, but there has also been a massive technical improvement in the last 12-18 months, and even in this season too. He has now become a great goalkeeper,” he added.
With De Gea’s contract expiring in June 2016, this time next year with the Spanish international will be free to speak to other clubs if his new contract isn’t signed and Neville has warned United to sort the situation out as soon as possible.
“Manchester United now need to get him signed up as he has become a big, big player for them, and when you get a goalkeeper like that, you have to keep hold of him.”
United captain Wayne Rooney has also been singing De Gea’s praises, the striker put United ahead against Liverpool just seconds after De Gea made the first of his saves from Sterling in the first half.
The 29-year-old even went as far as to say his team mate is now the best in the world.
“In my eyes he is the best keeper in the world,” said Wayne. “The performances he has shown for us have been fantastic. He is not as tall as some other keepers but his reach is really long.
“Sometimes in training you hit a shot and then turn away thinking it has gone in, but he just manages to get there and save it. I am delighted for him. He came through a tough patch early on in his career here and he is starting to prove what a top keeper he is now.”