Manchester United interim manager Ralf Rangnick said the club requires an "open heart operation" rather than "minor cosmetic" fixes if it is to revive its fortunes.
United named Ajax Amsterdam coach Erik ten Hag as their new manager to succeed Rangnick from the end of this season, with the 52-year-old signing a three-year deal.
READ | Who is Erik ten Hag, Manchester United's new manager?
United is sixth in the Premier League on 54 points from 33 games, three points and a spot behind Arsenal, which has a game in hand. The teams will face each other later on Saturday.
"You don't even need glasses to see and analyse where the problems are," Rangnick told British media on Friday.
"Now it's about how do we solve them? It's not enough to do some minor amendments – cosmetic things. 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 then it makes sense. I believe it doesn't take two or three years to change those things. This can happen within one year."
Rangnick described new manager Ten Hag as a "very good character" and said that the Dutchman would need strong leadership to support him as he tries to rebuild the squad.
READ | Outgoing Rangnick backs new boss Ten Hag to deliver at Man Utd
"The most vital part is that the club manages to get in the best possible players and we have the attitude, the energy," Rangnick added.
He said midfielder Paul Pogba, who is set to miss the remainder of the season with a calf injury, will not renew his contract with the club.
"As it seems right now, he will not renew his contract. Maybe the club or Erik will also not want to renew the contract, I don't know, but it's most likely he won't be here anymore next season," Rangnick said.