Manchester City manager Pep Guardiola said derogatory chants about Phil Foden's mother from Manchester United fans showed "a lack of class".
Speaking after an insipid and goalless Manchester derby at Old Trafford on Sunday, Guardiola said it was not an issue for United but for the individuals involved.
England international Foden was targeted by insulting chants during the first half of the Premier League match.
"Lack of class. But it's not United, it's the people, you know?" said Guardiola.
"We are so exposed, people who are on the screen in world football - managers, owners, and football players especially.
"Honestly, I don't understand the mind of the people involving the mum of Phil. It's a lack of integrity, class, and they should be ashamed."
The outcome of the game means City remain fifth in the Premier League, a point behind Chelsea in fourth, with United back in 13th.
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