That is according to Joleon Lescott, who shared a dressing room with Nasri at the Etihad for three years between 2011 and 2014.
Prior to the famous 6-1 drubbing of Manchester United in October 2011, Nasri was involved in a training ground fracas with Mancini.
Lescott revealed how the Frenchman told his manager to 'come outside' after offering up a scrap, taking shots at City coach Platt as well.
"He [Mancini] used to do the prep in the middle of the pitch and he's telling players what he wants," the former England international told That Peter Crouch Podcast.
"He's telling Samir Nasri to do what he wants him to do, but David Platt is on the side, and he's telling him to do something different, so he's half-listening to both and doing different things.
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"And then the manager lost his head and said: 'Samir, you're not doing it, go in.'
"Samir's gone in with no retaliation, so I'm thinking, that's not like Samir, Samir has got something in him to retaliate a little bit."
Lescott then went on to reveal that he eavesdropped on Nasri and Mancini's conversation later on, which turned a little bit heated to say the least.
"I heard Samir come in. He's gone: 'You [Mancini], outside. F******* outside now! You will never speak to me like that again. I'm not Mario Balotelli. Get outside.'
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"So Mancini is saying 'come into my office' and he's like 'no, I'm not coming into your office, get outside now!'
"He's calling him outside to have a fight with him. I'm just peeping! I could see from afar what was going on, me and one of the young goalies up there.
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"He is saying 'come outside, I'm gonna f*** you up, come outside, you will not speak to me like that again.'
"The manager has come in saying 'calm down.' And then Platty has come and said 'Samir, calm down'.
"He [Nasri] went: 'shut up, you're just here to suck his d***!'"
To no surprise, Nasri was subsequently dropped for the following match against United, which saw City run out 6-1 winners at Old Trafford.
Nasri, who had only joined the club that summer, would go on to enjoy a fine career at the Etihad as he won two Premier League titles and one League Cup across six years, though the last year was spent on loan at Sevilla.
After Pep Guardiola arrived in 2016, that spelt the end of the former Arsenal man's time at the club as the Spaniard complained about his physical condition.
Nasri and Guardiola never saw eye to eye and there was no way back, leading to his loan move to Sevilla before being sold to Turkish club Antalyaspor the following summer.