The ex-United captain worked closely with the 19-year-old during England's failed World Cup campaign in Brazil, and is confident that the youngster will be a success in the future.
Neville told the Manchester Evening News: "You are talking about real brilliant potential. The reason United spent £27m on a left-back at his age is because they see the huge talent and I can only endorse that talent.
"You have to watch him at close hand to realise that this is an incredible and hugely talented football player. Luke Shaw is fantastic."
United's summer spending so far also includes Athletic Bilbao midfielder Ander Herrera.