The German coach remarked that the Red Devils needed "open heart surgery" during his spell at interim boss at Old Trafford in 2022 and argues that the club's struggles under his successor Erik ten Hag prove that his comments were correct.
Rangnick told Norweigan outlet TV2: "I probably made that statement when the season was almost over about two years ago.
"It is probably only two or three weeks since Ten Hag was asked the same thing.
"Then he said that I was right in my analysis. I don't know how many players they have signed since, but it looks like I was right."
Rangnick made the comments after United were thrashed 4-0 by rivals Liverpool in April 2022 and declared that wholesale changes needed to be made at the club in order for the team to become successful again.
The coach - who is now in charge of the Austrian national team - said: "In medicine, you would say that this is an operation of the open heart. If this happens and everyone has realised that this has to happen and if people want to work together. I believe it doesn’t take two or three years to change those things, this can happen within one year.
"For sure [strong leadership is needed]. This is something that not one single person as a manager can do. In all areas you have to have top people and they have to work together in a very close, reliable way."