Rio Ferdinand has questioned Ralf Rangnick's work since he took charge of Manchester United in December.
The interim manager has won four of his eight games at the helm, suffering just one defeat to Wolves in the Premier League.
Rangnick's team have failed to impress, however, with many pundits criticising the form and body language of certain players.
The German has also been involved in a public spat with Anthony Martial, who wants to leave Old Trafford this month.
And Ferdinand isn't happy with the team's progress under Rangnick, seeing little improvement since the departure of Ole Gunnar Solskjaer.
Can Ralf Rangnick lead Manchester United to success? Let us know in the comments below!
"The manager talked in his first press conference about improving players and I’m still yet to see," said the United legend on his Vibe with Five YouTube channel.
"Has he had enough time on the training ground will be his argument I’m sure, but these players need improvement because they’re not doing it.
"Almost every player, to a man, is a shadow of their former self. I don’t see anyone going best the levels they were at before as yet."
Ferdinand went on to compare the first seven weeks of Rangnick's reign to Thomas Tuchel's start at Chelsea.
Tuchel, who was appointed by the Blues this time last year, got an immediate response from his struggling team and went on to win the Champions League.
"Great managers improve people," added Ferdinand. "We’ve seen what Thomas Tuchel’s done at Chelsea in that short space of time.
"We saw players elevate and become better players, consistently for a sustained period of time.
“[Antonio] Rudiger, before Tuchel came in, wasn’t even getting stripped. They were trying to sell him, his confidence couldn’t be any lower. He’s rejuvenated.
"[Marcos] Alonso has come while [Ben] Chilwell has been injured. Rejuvenated. Playing well. Reece James went another level.
"He created an environment where the players felt comfortable. You do need the results but you’ve got to start getting it from somewhere."
Rangnick has been involved in coaching and football administration for more than three decades, boasting an experienced CV.
Many, however, were concerned he wasn't an "elite manager" when he was appointed as United's interim boss.
Rangnick has won just two major trophies during his managerial career, with his last piece of silverware coming more than a decade ago.
"I look at him thinking he's not an elite manager," Arsenal legend Perry Groves told talkSPORT earlier this month.
"Ralf Rangnick is not an elite manager, his CV from Hannover, Schalke, Hoffenheim, and Leipzig, they're completely different entities to Man Utd. What's he won? The cup at Schalke and the Ligapokal at Stuttgart.
"He would have been under trial more with the players. We know when Antonio Conte went to Spurs, all those Spurs players are on trial and they're fighting for their future because he is elite and is a proven winner.
"It's the other way round at Man Utd... we sort of know who you are, we've heard of your name, but you haven't won anything, you're not an elite manager.
"And any interim that comes in, you've sussed the boss in two days. If you think that the boss hasn't got it, you're not going work your socks off for that boss. It doesn't work that way."
