Former England full-back Neville retired midway through last season to pursue a career as a media pundit, having himself won numerous trophies with United.
Both Neville and Giggs were members of the celebrated 'Class of 92' United youth side that spawned several first team regulars at Old Trafford.
But Wales winger turned midfielder Giggs was widely regarded as the cream of that crop and, at the age of 38, he could yet extend his record of English titles to 13 should United win the Premier League this season.
United manager Sir Alex Ferguson has already got Giggs to sign on for one more season but Neville said he had several more campaigns left in him.
"Will we ever see his like again? No, no way," said Neville.
"Ryan Giggs will go down as the most successful British footballer of all time and I cannot see anyone ever overtaking him. He's on the brink of his 13th league title, after all.
"When we were younger, we often heard about Alan Hansen's amazing eight championships with Liverpool. But what we are witnessing at the moment is greatness before our very eyes.
"Ryan is unique, he has surpassed all records in terms of domestic titles and he has incredible desire, quality and spirit. He's just fantastic to watch.
"You give up asking how long he could go on for. Why bother?
"When you see his quality and what a contribution he makes to the team why would he even think about it?
"Ryan is 38 years old, and he will contribute at the age of 42 if he wants to, the way his body is right now, the way his football is and the quality he still has."
Neville was speaking as part of a series of interviews carried out on behalf of the Premier League leading up to the end of its 20th season.
Giggs is the only player left who has featured in them all and Neville added: "The best player in the history of the Premier League? It's got to be Ryan Giggs, no question at all.
"He has constantly adapted his game.
"He went from being a flying winger in the early days to someone who could play off the front, to a central midfielder, and even to left-back if required.
"He can play anywhere and that's what really great players do: they adapt."
Neville added: "Ryan has a God-given talent.
"I first played with him when I was 14. He's still the best young player I've ever seen.
"It's astonishing what he could do -- the ball was tied to his feet and he could do everything at amazing pace.
"And, it's probably not the first thing you think of when you mention Ryan, but he's so tough mentally and physically very strong.
"He's got an incredible appetite and determination to keep working hard and win things every year."