The Manchester United boss claimed Sancho did not reach the levels necessary to be considered for a starting role in the side.
Sancho, however, has spoken fiercely against his manager.
The 23-year-old was not part of the group that travelled to the Emirates for Manchester United's 3-1 defeat to Arsenal.
Sancho did have flashes of encouragement as a false nine in pre-season. However, he has yet to start for United this season and boss Erik ten Hag has reasoned his decision to exclude the Englishman down to his performances in training.
"Jadon, on his performances in training we did not select him," he said.
"You have to reach a level every day at Manchester United and we can make choices in the front line. So for this game he was not selected."
Late goals from Declan Rice and Gabriel Jesus sealed the victory for Mikel Arteta's side, who looked much better on the day.
Rasmus Højlund's cameo off the bench showed some promise, and Anthony Martial starting did not do enough to leave a mark on the tie.
The former Borussia Dortmund star fired back at Ten Hag's comments after the game and took to social media to share his frustrations.
Sancho said, "I have conducted myself in training very well this week. I believe there are other reasons for this matter which I won't go into, I've been a scapegoat for a long time which isn't fair!"
He went on to claim that he will "continue to fight for this badge no matter what".
Ten Hag made the decision to send him to the Netherlands last season to deal with physical and mental issues for nearly three months, after which he was reintegrated into the side.
Sancho made 26 appearances in the Premier League last season, scoring six goals and providing six assists in that time.
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