Richard Dunne revealed Erik ten Hag's biggest problem following Manchester United's 3-0 Europa League defeat to Sevilla on Thursday night.
Mistakes from Harry Maguire and David De Gea over the course of the two legged tie meant the Spanish side advanced as 5-2 winners on aggregate.
The former Ireland defender isn't hopeful of Ten Hag receiving the transfer funds necessary to rebuild if the Glazers remain at Old Trafford.
Dunne highlighted the need for signings in several positions of the squad if Man United are going to be successful.
"They aren't going to get rid of David De Gea because he's doing okay (this season), that's not Man United. They should be looking for the best players," Dunne told Virgin Media Sport.
"The reality is finally hitting that they need a new goalie, a new centre back, more full backs, and they need centre forwards.
"So United need investment, and if the Glazers stay it's not going to happen for them. That's their biggest problem"
Man United's next game is against Brighton in the FA Cup semi final at Wembley on Sunday afternoon as they chase their second trophy of the season.
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