Manchester United must improve their squad in all areas except the goalkeeper if they are to compete, according to Ralf Rangnick.
Rangnick was placed in interim charge at Old Trafford following the dismissal of club legend Ole Gunnar Solskjaer in late November, though United's fortunes are yet to significantly change for the better.
The Red Devils sit three points behind fourth-placed Tottenham and level with Arsenal, who have played a game fewer, in the race for Champions League football next season.
Qualifying for Europe remains the only way for United to salvage their campaign, after elimination from all the cup competitions and failure to challenge Manchester City and Liverpool in the Premier League.
The likes of Paul Pogba, Cristiano Ronaldo and Harry Maguire have all been regularly scrutinised with regard to the problems at United, and Rangnick believes wholesale investment is needed in the squad.
The German boss also suggested the next permanent managerial appointment, with Ajax coach Erik ten Hag widely expected to take charge, will be key for United in the transfer market.
"The players have to give their very best no matter who the next manager will be, and if he's announced in one or two or three weeks, I don't think that this affects the current situation we're in," he told Sky Sports.
"But yes, of course, it's important to know who will be the new manager, because to start the recruitment process, to find the best possible players only makes sense if you know who will be the manager and how does he want to play.
"There might be a couple of players – and I have already named those players to the board – that independent of formation, from style of football, and independent of a new manager, that could be of interest for a club like United.
"But in general, if you look at the size of the way the team needs to be rebuilt, I mean, it's not enough to bring in three or four new players. It will be more, bearing in mind how many players will no longer be here with the contracts running out."
David de Gea has been a rare bright spark for a below-par United side this season, and Rangnick believes the goalkeeper is the only position that does not warrant significant improvement.
"Yes, I think apart from the goalkeeping, we need to make sure that we improve the squad in all areas," he added.
"To bring in players who really help the team to get better – again, it's about the profile. What kind of players do we need in order to play whichever kind of football we want to play?"
The former RB Leipzig head coach suggests United can learn from Liverpool, who they face on Tuesday at Anfield, regarding their investment and scouting.
"With Liverpool, it's clear why they are playing as aggressive as they do – it's since Jurgen [Klopp] arrived," he continued.
"If you compare the squad that he inherited six years ago and compare it with the present, I think there are maybe four or five players still there.
"All the others signed since then have been signed exactly under those premises: how do we want to play? They have to be able and willing to run and sprint a lot. They have to be physical. They have to be technical. They have to be clinical. The profile for each position has been clear and that's why they are where they are.
"And here at Manchester United, this hasn't been the case with every change of manager. New players came in, but it was not under that pre-condition of how do we want to play, and this is for sure something that needs to be changed in the future, but this doesn't help us.
"Now we have to play with the players that we have available and get the best out of them. It will be difficult for us at Anfield. We know that we have to raise our level to the highest possible that we can.
"Our ambition is to win that game, and this is how we are going into it."