Speaking on Sky Sports, the former Red Devils captain said the club's recruitment had been "disjointed" following Sir Alex Ferguson's departure as manager in 2013 (h/t Max Winters of MailOnline).
"If you look at that back five today then they were all there when Sir Alex Ferguson was at the club.
"They've signed eight defenders in the last four or five years and not one of them is in the team today.
"You've got Valencia, Jones, Smalling, Young and De Gea and you obviously have Lingard and Rashford, who were also at the club as well, so seven out of that 11 were there five years ago.
"The recruitment has not been good enough in the previous five years. It's been disjointed when David Moyes came in, then they flipped upwards towards Louis van Gaal and then backwards with [Jose] Mourinho in terms of the profile of players.
"It hasn't been good enough, the recruitment, it's been all over the place and you can see still quite a lot of the players in that squad have been at the club for a long time."
United have been forced to execute several layers of squad rebuilding since 2013, and the post-Ferguson players have taken their time bedding in.
The Glazer family, the club's owner, has allowed the club to spend a chunk of its revenue in recent seasons to help Mourinho build a competitive side, but a number of positions continue to lack top-class quality.
United's creativity remains frustrating under The Special One, and the starting XI is often functional rather than entertaining.
The team's successes in the UEFA Europa League and EFL Cup last term displayed Mourinho's trophy-winning potential to United supporters, but issues remain, with Manchester City running away with the Premier League crown this term.
Italian outlet Calciomercato.com reported United might consider Blind's departure as Mourinho attempts to revamp his squad in January (h/t the Mirror). The Dutchman is set to become a free agent next summer, forcing United to consider a sale during the upcoming transfer window.
Blind has made just four appearances in the Premier League this season but was used in every match during the UEFA Champions League group stage—starting six times.
Per the Mirror, Mourinho has previously explained he is willing to sell talents who aren't happy under his stewardship, saying:
"I think for the right price. That's my approach as a manager, in cases where the club advises me.
"I think every player has a price. If a player is not happy, if a player brings with him the request with the number that we consider a good number for us—like it happened for us last season with Memphis Depay and Morgan Schneiderlin—I would never say no."
Blind is a useful squad player, but at 27, the former Ajax man likely wants regular first-team football.
The defender doesn't have the dynamic pace or physicality required for Mourinho's tactics, so a transfer would make sense.
United remain short of a necessary world-class talent in midfield. Blind's sale could help the Red Devils tempt a new signing in January to assist Paul Pogba in the centre, as Nemanja Matic sits deep.
Ander Herrera has been used to deputise for Pogba during the Frenchman's absences this term, but the Spain international lacks a dynamic edge to his creative game.