Neville sees no reason why the 38-year-old cannot go on way beyond the additional season Sir Alex Ferguson has already got him to sign a contract for.
"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."