Ole Gunnar Solskjaer targeted youth at Old Trafford and drafted in 22-year-old Wan-Bissaka from Crystal Palace, while they also added Dan James, 21, and Harry Maguire in a £150million summer spending spree.
Meanwhile Trippier swapped Tottenham for Spain and joined Atletico Madrid for £20million, some £30million more than United paid for Wan-Bissaka.
And Walsh, who was sacked as Everton’s director of football in May 2018, thinks United should gone for Trippier instead of their current right-back.
Walsh, who uncovered the likes of Riyad Mahrez, Jamie Vardy and N’Golo Kante while at Leicester, told The Athletic: “United have made a lot of signings. Look at £50million for Aaron Wan-Bissaka.
“Now, perhaps it is too early and he will improve, but my eyes tell me when he gets the ball he is not the best. He is a good athlete and very quick, strong, and a good defender, but United don’t need a good defender, they need someone who can play, get on the ball.
“If I had been at United, I would have said, ‘Put your £50million away, go and get Kieran Trippier for half that. He is an England international.
“He isn’t a great defender or a physical specimen, but he can play right-back and get the ball in early and you have strikers who can score goals.’ It is common sense.”