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Match of the Day analysts Alan Shearer and Ian Wright were among those to condemn the action, while ex-Manchester United defender Gary Neville called on Aguero to apologise.
Guardiola defended Aguero in the aftermath of the game and once again backed his striker, who he said would have said sorry had Massey-Ellis complained.
"I didn't speak to Sergio about this, but I'm pretty sure if she felt bad, he will apologise without a problem," Guardiola said.
"All the people looking from outside judge, but I know the intention from Sergio. Sergio put his hands in a normal way, like he does many times to me, on or off the pitch.
"Or when I hug him, when there is a substitution, or when sometimes he touches the referee as well or an opponent.
"If I'd seen some aggression, maybe. But I think it was normal as I know him perfectly. He's been a huge star in the world, but he's humble, one of the nicest people I've met.
"What is important is his intention, and his intention was normal, to talk to her in a normal way. It was not a bad word, it was just normal."
Guardiola likened the reaction to the one Bernardo Silva received for a controversial social media post involving team-mate Benjamin Mendy last year.
Silva apologised after posting a picture of a cartoon character promoting a chocolate brand in Spain next to a photo of Mendy with a caption reading: "Guess who?"
The apparent reference to Mendy's race led to a one-match ban and a £50,000 fine, while Silva was ordered to undergo educational training.
"It's the same with what happened with Bernardo. I know him perfectly well, it was a joke and this was a normal situation," Guardiola added.