Neville, who confirmed midweek he would not be working at Old Trafford in 2014-15, was on David Moyes's coaching staff as United finished seventh in the standings - 22 points adrift of champions and arch-rivals Manchester City.
Moyes paid the ultimate price for United's failure after he was sacked in May but Neville said the Scot was not the only man at fault for the club's poor performances.
"I was involved last year and last year was an absolute disaster," he said.
"It was an absolute disaster from start to finish we must all take responsibility, not just David Moyes. I take responsibility and so does everyone involved."
Van Gaal has since taken charge, guiding the club to five consecutive pre-season wins on their tour of the United States and Neville believes the former Netherlands boss can win the league in his first season at the helm.
"I think we're going to win the league. I'm sure that's what Louis van Gaal will be saying to the players because second isn't any good at Manchester United," he added.
"For United, it's finishing top, as Premier League champions. It's about regrouping and all the lads have come back for pre-season and they look like they're ready to win the league again.
"We've got a great chance this year because there's no European football so we can concentrate solely on the league.
"And from what I saw in pre-season and the support we had, the club keeps getting bigger and bigger, and I think we're on the right road again."