Scholes told BT Sport: "I just think when you look at the game, there's a real lack of quality in the middle third and the final third.
"Again, Wayne Rooney looked like the only player who could get something for Man United, but the quality into him was just not good enough.
"You have to give great credit to Swansea I think. It's a great performance for them to come here and win on the opening day of the season, but Van Gaal knows now that he needs [new] players. I think he probably knew that beforehand but he knows it more than ever now."
United's next game will be next Sunday away to Sunderland.