Wayne Rooney officially retired as a player in January 2021 when he was appointed manager of Championship side Derby County on a two-and-a-half-year contract
But the club is set to go five years without a trophy, after losing to Atletico Madrid in the last 16 of the Champions League in March.
They are seventh in the Premier League and three points behind fourth-placed Tottenham in the battle to secure Champions League football next season.
Rooney described United's 2021-22 campaign - in which Rangnick replaced the sacked Solskjaer in November - as a "strange season".
"I have been [to watch Manchester United] a few times and it looks like a team of individuals," Rooney said.
"They would want the season to stop now and forget about qualifying for the Champions league. They are not going to compete next season in the Champions League.
"They have to rebuild and put themselves in a place, in three years time, where they can challenge again for the Premier League."
The future of France midfielder Pogba, who re-signed for £89m in 2016, remains uncertain with his contract expiring at the end of the season.
Meanwhile, 37-year-old Ronaldo returned to Old Trafford from Juventus last August on a two-year contract.
"It would be better for Paul Pogba to move on," Rooney said.
"He hasn't had the impact he would have liked. He's looked a completely different player for France. It hasn't quite worked at Manchester United. There are few players they need to let go.
"Ronaldo has scored important goals but looking to the future of the club you have to go with younger, hungry players. Cristiano is getting on a bit, that is football. He is a goal threat but in the rest of the game they need more."
Captain Harry Maguire has received criticism for his club performances this season - however Rooney thinks the centre-back can still be "a big part" of the club's future.
"I like Harry," Rooney said. "He hasn't been on his best form like a lot of players but for England he looks like a world-class centre-back. If he can get his confidence back he can be a big part of [the rebuild].
"They have good young players. I think Jesse Lingard should be playing, he brings energy and quality. They just have to get them confident, get them believing."
-- Courtesy of BBC Sport