The quality is not there at United - Scholes
United's shock seventh-placed finish last term means they are playing no part in this season's elite European club competition – something that has not happened since the 1995-96 campaign.
And the Old Trafford outfit made a poor start to the new Premier League season on Saturday as goals from Ki Sung-yueng and Gylfi Sigurdsson gave Swansea City a surprise 2-1 away win.
New United manager Louis van Gaal gave 20-year-old defender Tyler Blackett a Premier League debut in his favoured 3-4-1-2 formation, but he was forced to switch systems at the break and play Ashley Young as a left-back.
United's defensive frailties were evident during the match, but former midfielder Scholes felt the entire side struggled, particularly in midfield.
"It wasn't good enough," Scholes told BT Sport.
"When you miss the likes of [departed defensive trio Nemanja] Vidic, [Rio] Ferdinand and [Patrice] Evra…you saw defensively, they were inexperienced and just got caught too many times.
"In the midfield area, the quality just wasn't there. When you've got strikers like [Wayne] Rooney and [Javier] Hernandez…there's nothing to feed off.
"When they got the goal [Rooney equalised in the 53rd minute] you expect United to go on and score one, two, three…but you never got that impression."
Scholes, who made over 700 appearances for United, is disappointed by the club's inability to attract stars to the club in the transfer window, despite the likes of Ander Herrera and Luke Shaw joining in the close-season.
And he feels that Toni Kroos and Cesc Fabregas, who have moved to Real Madrid and Chelsea respectively, would have been excellent additions to United's squad.
"There's no doubt there's a massive improvement needed from these players if he [Van Gaal] doesn't spend," he added.
"The two quality players who haven't come here and gone to other clubs, Toni Kroos and Cesc Fabregas, would have made a huge difference here."