Rangnick had a short spell at United as caretaker manager after Ole Gunnar Solskjaer's dismissal in season 2021/22.
He told Canal+: "There were some fundamental things that needed to be changed and since then they have spent £700 or £750 million on new players . And they are in a much worse position in the league table than they were then!
"They could even save the season by winning the Europa League, because they will be in the Champions League. Everything else will be a disappointment and it will be interesting to see what happens."
Sympathy for Amorim
Indeed, despite the criticism, Rangnick concedes the season can be rescued through the Europa League.
He added: "They hired a manager (Ruben Amorim) halfway through the season who plays with a three-man or five-man defence, but the team is built around a four-man defence.
"That's what you see when you look at the way they play, especially in the Premier League, against teams that Manchester United would normally be able to beat. Of course, in the Europa League – usually with that result against Lyon you're out – they managed to turn things around, but the stadium has had a significant impact."