Arnold Muhren, who starred for both United and Ajax as a player, believes they have problems all over the pith and says the money at Old Trafford needs to be spent on an entire ‘rebuild’.
De Ligt, 19, who opened the scoring for Ajax against Tottenham in the Champions League on Wednesday night, is one of the most highly-rated defenders in world football.
Barcelona remain the favourites to sign him having already secured a deal for Ajax team-mate Frenkie de Jong to move to the Camp Nou in the summer.
And Muhren thinks a switch to Barca makes sense and has urged United to concentrate on other targets as they look to turn their fortunes around.
“Ajax have a very good connection with Barcelona,” he told Love Sport Radio.
“A lot of Dutch guys went to Barcelona, one or two came from Barca to Ajax.
“So the relationship is very, very good. De Ligt can play in any team. There are a lot of teams interested in him.
“But I saw the Barcelona game yesterday [a 4-0 defeat by Liverpool in the Champions League] and they need something at the back desperately because there are one or two players a little bit over the hill.
“Barcelona need a lot of good defenders and they need De Ligt.
“I understand Manchester United are willing to spend a lot of money on foreign players and if De Ligt chooses to go to Manchester United, it’s of course a very good move for him.
“But I think they need more players than just De Ligt. They have to rebuild the team.”
United boss Ole Gunnar Solskjaer is set to overhaul his struggling squad after they failed to qualify for next season’s Champions League.