Ralf Rangnick hit out at the Manchester United supporters who hurled abuse at Paul Pogba during Saturday's victory against Norwich City.
The France international was substituted in the 74th minute, replaced by Marcus Rashford moments before Cristiano Ronaldo completed a hat-trick to secure a 3-2 win at Old Trafford.
Interim boss Rangnick said he did not immediately hear the chants of "F*** off Pogba" that came from the stands, but he said fans should not isolate individuals.
Pogba, a World Cup winner with France, is expected to leave United at the end of the season when his contract expires.
That will bring to an end a largely underwhelming six-year stint back at the club where he began his professional career prior to spending four years at Juventus.
Pogba cupped his ear to the United fans at one point and appeared to hear their taunts as he returned to his seat among the substitutes and club staff, even if his manager had his focus elsewhere.
"I didn't hear it myself, but I was informed after the game," Rangnick said. "I can fully understand the fans are frustrated, so are we, but I don't think they should take on individual players. I don't think that is right or correct."
Rangnick was delighted with Ronaldo for scoring the 50th hat-trick of his club career, and his third across two spells with United. An incredible 44 of those trebles came for Real Madrid, with the other three arriving during his Juventus career. Ronaldo's second goal, a header, and his third, a long-range free-kick, were described as "brilliant goals" by Rangnick.
Ladies and gentlemen, Cristiano Ronaldo. pic.twitter.com/ujTzg1fKma— Manchester United (@ManUtd) April 16, 2022
But Rangnick warned United must improve significantly if they are to take anything from their next two games, which come away from home at Liverpool on Tuesday and at Arsenal on Saturday.
The German boss complained about United's defending, which allowed Norwich to battle back from two goals down to draw level early in the second half.
Ronaldo's salvage operation, on a day when Tottenham and Arsenal both lost, meant United suddenly find themselves firmly back in contention for fourth place and a spot in next season's Champions League.
However, Rangnick told MUTV: "With a draw, it would have been a disaster for us, not only in the table but also with regard to the atmosphere in the locker room.
"We have to focus on our own performance. The result was good and should lift the momentum and the confidence of the team, but we have to be realistic; with that kind of performance it would be almost impossible to get something out of the away game against Liverpool and also away at Arsenal, and at home against Chelsea [on May 15] it will be difficult.
"We're still in the race, but we have to lift our performance and our level."
Goalkeeper David de Gea said the result was "massive for us" and commended Ronaldo, saying on NBC: "Sometimes people just count goals, but I think he's playing very well and he scored three important goals for us again."
Like his manager, De Gea is not taking a blinkered view of United's performances.
"We are conceding a lot of chances," De Gea said. "I think Norwich played a great game. But I think it's more us. We are not playing well. We should control the game more, especially against Norwich at home, but in the end we got three goals from Cristiano and the three points.
"We are happy, but we know we have to improve a lot."