Manchester United boss Erik ten Hag said he left Cristiano Ronaldo on the bench during the side's 6-3 defeat to Manchester City "out of respect".
The Portuguese star was an unused substitute at the Etihad Stadium despite United trailing 4-0 down at half-time, while Victor Lindelof, Anthony Martial, Fred, Casemiro and Luke Shaw were summoned off the bench.
Speaking after the match, the Dutch manager explained he did not want to put the 37-year-old through the humiliation against their bitter rivals.
"I wouldn't bring him in because out of respect for [Ronaldo], for his big career," he said.
"And the other thing was the advantage I could bring Anthony Martial, he needs the minutes but I don't want to point it out like that."
Ten Hag also lamented the Red Devils' "lack of belief" in the Manchester derby, which saw Erling Haaland and Phil Foden bag hat-tricks for the defending champions.
"When you don't believe on the pitch, then you can't win games, that is unacceptable. We get undisciplined at following rules, and you get hammered.
"For me, it was a surprise. We were not on the front foot, we were not brave on the ball, and there were spaces to play, but we were not brave enough.
"All the credit to City, but it's nothing to do with City, our performance was not good. It had to do with the belief as individuals and as a team.
"In this moment I can't think about positives. We let our fans down, we let ourselves down and we're hugely disappointed."