Sanchez failed to exert much influence in a red shirt once again as United were eliminated from the Champions League last-16 in a 2-1 defeat to Sevilla at Old Trafford.
The Chilean has struggled for consistency since arriving from Arsenal in January and laboured on Tuesday night after replacing Marcus Rashford on the left flank.
Rashford, despite his match-winning performance on the left-hand side against Liverpool, was moved out to the right in order to accommodate Sanchez, but neither player appeared to benefit from the switch.
Mourinho admitted last week that United may only begin to see the best of Sanchez next season and Scholes believes the 29-year-old should be sacrificed if his performances are not up to standard.
“Rashford was frightening on that left side on Saturday, but he moved him to bring Sanchez into what he thinks is his best position,” the former United midfielder said.
“[Sanchez] gave the ball away so often and his manager has to see that in the 10 games he has played, he has not been good.”
Mourinho has Jesse Lingard, Juan Mata and Anthony Martial all vying for regular starting spots in attacking midfield positions as well as Sanchez and Rashford.
“He needs to choose his best front three and be brave enough to leave one out,” Scholes said. “At the moment, Sanchez is the one to leave out.”
Appearing as a pundit on BT Sport, Scholes also criticised United’s all-round performance, accusing Mourinho’s players of lacking desire and energy.
“It's difficult to describe how bad that was,” he said. “Lethargic, bad attitude… [Mourinho] said in his interview he was happy with their attitude, but he has to be protecting his players.
“The players have let him down tonight by being so mediocre against a poor team. You are going for a place in the Champions League quarter final and there was no desire, heavy legs.
Scholes added: “It was poor. You can accept an off night if the attitude is right, but it wasn't.”