David Moyes' and United's season sunk to a new low on Tuesday night with a dreadful 3-0 loss to rivals Manchester City at Old Trafford.
With players failing to perform, and the Reds languishing in 7th place, former captain and current England assistant Gary Neville believes handing another blank chequebook to the former Everton boss isn't the solution.
"The worrying thing is people think the right answer is just to go and chuck another £150million at it," Neville told Sky Sports.
"But it's almost like you've got to know what's wrong with the soup before you throw more ingredients in to make it better - and at the moment I'm not quite sure where you'd start."
United spent £80 million on players over the summer, seeing just three players, all midfielders, coming in to the club.
Wilfried Zaha barely featured for the Reds in the first half of the season, before being shipped out to Cardiff on loan. Marouane Fellaini, the big summer recruit that followed Moyes to Old Trafford, has hugely failed to replicate his Everton form, struggling with niggling injuries and looking a longway short of the class expected of a near £30 million midfielder.
Even Juan Mata, so impressive for Chelsea over the previous two seasons yet frozen out by Jose Mourinho this year, has flattered to deceive since a club record £37 million move to United. Given his desire to play a similar role to Rooney, where the scarcely used Shinji Kagawa is already waiting in the wings, there were questions whether such a signing was really the necessary one.
To some extent the Mata move was the first desperate action of Moyes and the Glazers, ready to pin their hope on a quality player's arrival reigniting their season despite it not really being the best move for club or player.
"The idea that United need to spend a load of money is very well," Neville continued. "They've got money, but they have spent £80million already on Zaha, Fellaini and Mata in the last eight or nine months.
"It's not going to be a case of just throwing a load of money at it. They've got to get the actual signings right and get the recruitment right.
"In the summer they wanted players of the quality of Fabregas, Bale, [Leighton] Baines and Ronaldo. Those types would have been fantastic and would have given everybody a lift.
"They didn't end up getting them and that was the problem."
Blowing further hefty fees on good players that won't necessarily fit alongside what they already have is clearly what Neville is afraid of, and may be an even greater setback to the club than David Moyes' already troubled reign as manager.