The Red Devils were 2-0 up and cruising against the Spaniards courtesy of a brace from Bayern Munich loanee Marcel Sabitzer, but the last 10 minutes of the tie saw both Tyrell Malacia and Harry Maguire net own goals to give Sevilla plenty of hope ahead of next week's second-leg on their own patch.
Following the full-time whistle, Scholes declared that the changes Ten Hag made played a large part in United's second-half demise. The former Red Devils ace was covering the clash as part of BT Sport's punditry team when he made the bold claims.
"Manchester United were very quiet in the second half, didn’t really create anything, substitutes I don’t think helped the game - it definitely weakened the team," the United icon claimed. "You can understand Martial with him being fragile but really sloppy in that second half.
"Two two, still - look, injuries and suspensions won’t be great for next week - but I felt we saw enough to say Sevilla aren’t a great team and United should still have enough, but I tell you what, going over there will be difficult."
He later added: "The second half was a complete disaster, really."
While Scholes seemed firm in his stance that the changes were what sparked the capitulation, Ten Hag has hit back and is adamant his hands were tied.
"We had to make some subs with injuries," the Dutchman complained. "Rapha [Varane] at half-time. Also, Anthony Martial, we had to sub him because it was his first game after [injury] - his first start.
"Antony as well, and Bruno [Fernandes] because they were close to a second booking. So we had to make some subs and then lose control in the unlucky moment [Sevilla's first goal]."
Sevilla's second goal came while United were down to 10 men, with Lisandro Martinez coming off injured after the hosts had already made the maximum amount of substitutions permitted.
Ten Hag insisted that Sevilla's equaliser was mainly due to bad luck on United's part, though conceded his players could still learn something from the situation.
"We have 10 [men] and we conceded two own goals. It was bad luck and we have to deal with that. Of course, we have to learn, we have to kill the game but still everything is open for the next game."