The former Liverpool defender has criticised the United boss's handling of the Arsenal forward.
Carragher believes Manchester United will one day regret selling the 23-year-old for £16 million as he has pace and youth on his side.
"It makes you wonder, then, why Van Gaal was so quick to offload Danny Welbeck to Arsenal. Van Gaal was brutal when saying the England striker was ‘below United’s standards’, but doesn’t the manager have a reputation for improving young players?" Carragher wrote in his weekly Daily Mail column.
"Welbeck might not have the pedigree of the others but he has got pace and youth - qualities United could do with - and his total of six goals for Arsenal already is as many as Falcao (one), Van Persie (two) and Rooney (three) have scored between them so far.
"Like United’s defenders, Welbeck’s best years are in front of him and that decision to sell him may one day be a cause for regret. If the present is about how Van Gaal organises his defence, the future is going to be about how he replaces his attack. It won’t come cheap."