The former Red Devils midfielder emerged from the 'Class of 92' to play a key role in United's successes over the next two decades.
And Scholes is concerned that United will find it just as tough as Liverpool have to get back to the top, should they leave it too late to cure the team's current ills.
A home defeat to Swansea on the opening day of the Premier League campaign suggested new manager Louis van Gaal has plenty of work to do in order to improve even on last season's miserable performance, when United trailed in seventh in the top flight.
Scholes claims he was asked last season, when working on the Old Trafford coaching staff, whether United should move for Cesc Fabregas or Toni Kroos over the summer.
In the end, Fabregas left Barcelona for Chelsea and Kroos departed Bayern Munich for Real Madrid.
It is not known whether United made a formal offer for either midfield player.
"Either way," said Scholes, in his Independent column, "the situation now, with 11 days of the transfer window left, has become ever more desperate for my former club. They have to sign some quality players.
"I am scared for United. Genuinely scared that they could go into the wilderness in the same way that Liverpool did in the 1990s."
He added: "What do United need? Five players. Not five players with potential. Five experienced players... for now. Five proper players who can hit the ground running and turn around a situation that looks desperate.
"United's forwards are as good as any team in the league. The problem is what comes behind them."
Scholes identified the Real Madrid quartet of Xabi Alonso, Sami Khedira, Raphael Varane and Angel Di Maria as players he would target, along with Borussia Dortmund and Germany centre-back Mats Hummels.
Insisting United's chief executive should take the initiative, Scholes added: "Ed Woodward keeps telling us that the money is there. I would say that now is the time to start spending it."