That’s according to the club’s former head of youth recruitment, Derek Langley.
The Ajax duo have impressed this season with De Jong sealing a summer switch to Barcelona.
And the future of De Ligt is uncertain with the likes of Barcelona, Manchester City and Manchester United all linked with the 19-year-old.
But Langley has revealed the Red Devils previously turned down the chance to sign both of them.
He told the Manchester Evening News: “Players that they turned down? Matthijs de Ligt. We had God knows how many reports on Matthijs de Ligt.
“Frenkie de Jong and all these players now are sort of around Europe.
“Dayot Upamecano, who is now at Red Bull Leipzig, was another.”
“This was one of the reasons why I had a meeting with Ed Woodward and I told him that I wasn’t convinced with the competency of certain people at the club.
“I told Ed Woodward quite straight: ‘If you think I’m going to sit here and just tell you what you want to hear, I’m not that man because I’m going to tell you exactly how I see it’.
“I think it was possibly part of my downfall as to why seven months down the line I was removed because I wouldn’t tow the line in relation to telling them exactly what I thought.
“It’s one of them things in football – you come to accept it.
“Manchester United thanked me for the time I spent there and the players I’d taken in, but ultimately we could have been so much better if people had listened.”
United are expected to overhaul their squad this summer.
But former boss Louis van Gaal does not think De Ligt will make the switch to Old Trafford.
“De Ligt at Juventus? I think De Ligt can play in any competition,” Van Gaal told Ziggo Sport.
“In Italy they are the masters of defence, so he can best develop there. If I had the chance I would go to Barcelona.
“They have central defenders who are not too good, so he will play there. Or I would go to Manchester City.
“I don’t think the central defenders are that great either, so he’ll play there too.”