The former midfielder described the Spain international’s contribution to the hosts’ third goal as “criminal”.
United trailed 2-0 at the time, having conceded twice early on, and the game was effectively put beyond their reach when Justin Kluivert flicked home a cross from the left.
Scholes, though, believes that De Gea should have acted more decisively in order to stop the young Dutchman scoring.
“He bottles it, doesn’t he?” Scholes told BT Sport. “Basically, he’s scared of getting himself hurt.
“De Gea, even as a goalkeeper, make yourself as big as you can. You might get smashed in the face, you might get injured but he turns his back away. He actually makes himself smaller. It’s criminal. For such an experienced goalkeeper, it’s criminal.”
The ex-England man did note, however, that the goalkeeper was not alone for blame.
“The ball should never go across the box like that,” he continued. “Harry Maguire looks wooden, he’s very stiff.”
De Gea has found himself at the centre of an unwanted media storm in recent months, with the former Atletico Madrid man’s level having been questioned.
Manager Ole Gunnar Solskjaer, though, appears determined to stick with the Spain international, despite pressure to play Dean Henderson, who excelled during a loan spell with Sheffield United last term.
On Saturday, the boss faces making that big call again with Manchester City the visitors to Old Trafford in a match that will once again put his management under the spotlight.
The Red Devils currently lie sixth in the Premier League, one point better off than their neighbours, and only five behind leaders Tottenham. In addition, United have a game in hand.