Erik ten Hag warned Alejandro Garnacho that his previous performances this season were "not good enough" after the Manchester United teenager scored in Tuesday's League Cup win against Crystal Palace.
United eased the pressure on Ten Hag as they followed Saturday's 1-0 success at Burnley in the Premier League by beating Palace 3-0 in the third round at Old Trafford.
Garnacho put United ahead with a clinical first half strike from Diogo Dalot's cross, before Casemiro and Anthony Martial completed the comfortable victory.
The 19-year-old began United's first two matches of the season, but his appearance against Palace was the first time he was named in the starting line-up since a defeat at Tottenham five weeks ago.
"You have seen at the start of the season we played him and then his contribution was not good enough," United boss Ten Hag said.
"He has to learn when he does his job in defending he will always have his moment and he will always be decisive because he has great qualities.
"As well, it's not only off the ball. But I want to see like today, he is entering the box in the right spot to finish.
"Everyone likes him, the fans like him, the team likes him, I like him but we also have to demand from him and push him because he can act on a very high level. He has to show it every day."
Ten Hag was more impressed by Morocco international Sofyan Amrabat, who filled in at left-back on his first start for the club, before stepping into his preferred midfield role after half-time.
Amrabat joined United on loan from Italian side Fiorentina on transfer deadline day and Ten Hag is delighted by his versatility.
"Sofyan is a player, and that was one of the reasons we signed him, where the team needs him, he will play and he can play in more positions," he said.
"Every player has his best position but he gives a certain dynamic in the game. We have seen today but also for him and many players, we just started."
Ten Hag refused to answer questions about Jadon Sancho after a report in Germany said the United winger's poor form was partly due to long sessions playing X-Box computer games.
Sancho has been training away from United's first team after angering Ten Hag when he wrote on social media that he was being made a scapegoat following the Dutchman's decision to leave him out of a match at Arsenal earlier this season.
"I don't talk about personal issues and I don't talk about players who are not available," Ten Hag said before concluding his press conference.