Keane slammed vice-chairman Ed Woodward, and inexperienced defenders Chris Smalling and Phil Jones, after United's worst finish (seventh) in the English top flight since 1989-90.
A United midfielder of 12 years, Keane said disgraced boss Moyes was made to be the scapegoat of a wider problem - recruiting - as he put the blame for United's struggles at the feet of Woodward.
"He (Moyes) had one transfer window, and it's not always down to the manager when players don't come in," Keane said, speaking at ITV's World Cup launch.
"I think Ed Woodward needs to look at himself. He's got to get deals done.
"I think he (Moyes) should have been given more time. I was happy with David Moyes.
"I think (Louis) Van Gaal is a good choice. Only time will tell. He's managed big clubs."
Keane particularly lamented the signings of Smalling - from Fulham - and Jones, bought off Blackburn - both deals done prior to the infamous Moyes era.
"They've had a platform for the last couple of years," he said.
"We were told two or three years ago Jones was going to be the new Duncan Edwards, Smalling was this… I've watched United live nine, 10 times this year and they have been none of those things.
"If anything I think they have gone backwards.
"I've actually been a big fan of them – yes, give them a chance, you say you have to give players a chance to mature but also you've got players who you say we've given you a chance and you're not taking it.
"They need to do a lot better if they want to cement their place at Man United and United to win trophies. Jones needs to toughen up.
"Every time I see him he is getting carried off. He's got to toughen up – he's playing for Man United. They have to recruit in the summer – they might get two."
Keane said a strong line-up through the middle was what United lacked, as they finished below the top-three for the first time in 23 seasons.
"It's the spine of the team. United have come up short defensively and in the middle of the park they have not done enough," Keane said.
"You watch any of the teams that are winning trophies… I'm stating the obvious, you've got to have a strong spine, goalkeeper, defender, midfielder and striker and United have been short in two of those areas.
"It makes it very difficult to win trophies."
