Graeme Souness insists it will take years for Manchester United to be challenging for top honours again.
United were knocked out of the Champions League on Tuesday night as they were beaten 3-0 by Barcelona .
Ole Gunnar Solskjaer's men also face a battle to make the top four, with United two points off Arsenal with five games to go.
They face a crunch clash at Everton on Sunday before the Manchester derby in midweek with the two matches likely to go a long way to determining their fate.
But Souness believes Solskjaer has a "massive job on his hands" in the coming years.
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"People will think I'm coming at this from being anti-United, but not in the slightest. There is no quick fix," he said on Virgin Media Sport.
"Right now, what you are looking at, unless they have a stream coming through the youth system, they will have to go big, big, big in the transfer window. They are not going to do it in one transfer window.
"From the team that started in Barcelona, how many can you say are going to be in that team and be the main men in that team for the next five years?
"There are a lot of positions there that need to be looked at and you don't solve all of them in one transfer window."
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Ole Gunnar Solskjaer is likely to be given around £250m to strengthen this summer with four new signings lined up.
A central defender tops his list of priorities although they face a battle to land top target Matthijs de Ligt.
England youngsters Jadon Sancho and Callum Hudson-Odoi are also on Solskjaer's radar, as is Crystal Palace right-back Aaron Wan-Bissaka.
