Speaking on BT's coverage of United's Champions League defeat to PSV Eindhoven, Scholes feels van Gaal has got it wrong in not bringing in enough strikers this summer.
Van Gaal sanctioned the departures of Robin van Persie and Javier Hernandez to Fenerbahce and Bayer Leverkusen respectively, and opted against making Radamel Falcao's loan from Monaco into a permanent deal.
United spent big again in the summer, with the likes of Memphis Depay, Bastian Schweinsteiger and Morgan Schneiderlin all coming in, but only one recognised striker was signed when Anthony Martial arrived on transfer deadline day from Monaco.
Scholes believes, with Wayne Rooney currently sidelined through injury, United's transfer activity has ultimately left van Gaal's side unbalanced and short of goals.
"The one thing with the United squad now is that they're short of goals," Scholes told BT Sport.
"Short of real top quality centre forwards who guarantee you goals. Van Gaal spoke last year about his squad being unbalanced and I think it's even more unbalanced now without top strikers.
"They've let three or four strikers go. I think if we'd have kept a Van Persie or a Hernandez it looks quite strong.
“They can score goals. Martial could be a real threat coming off the bench. I just think that's a mistake."
United were able to put three goals past arch-rivals Liverpool at Old Trafford on Saturday, but that was the first time they had managed to net more than once in a Premier League fixture this season.
Firepower is clearly needed if the Red Devils are to challenge for top honours domestically and respond positively to their opening group stage setback in Europe.