Filippo Mancini stunned coach Andy Welsh when he ignored his instructions 10 minutes from time against Liverpool reserves on August 10.
Mancini's youngest son Andrea had already come on for the Elite Development Squad as a second-half substitute when the amazing incident took place at Hyde United's stadium.
Refused to come on: Filippo Mancini, son of City's Italian manager
Night of shame: Carlos Tevez (third left) on the bench at Bayern Munich
Welsh ordered Filippo to come on in the pre-season friendly, but the Italian refused and watched the rest of the game from the sidelines.
The revelation compromises Mancini in his fierce dispute with Tevez after the City striker appeared to ignore the manager's instructions to go on against Bayern Munich.
Tevez, suspended for two weeks pending the club's disciplinary process, refutes that claim. A group of his City teammates will tell an internal investigation that they did not hear him refuse to play.
Mancini questioned his professionalism, but it now appears his own son's attitude is also under scrutiny. Andrea came on against Liverpool in the 60th minute, but Filippo was so incensed at being overlooked that he refused to go on.
Centre of attention: Roberto Mancini takes City training on Friday
A City official said: 'Filippo is a non-contracted, unpaid player who was on the substitutes' bench for the non-competitive game.
'In these circumstances, a disciplinary procedure would have been invoked. However, as he was not an employee of the club, this was not a viable option.
'The matter has been dealt with internally. Roberto Mancini was not aware of this incident.'
Filippo joined City on loan from Inter Milan in 2008 but failed to break into the first team. He returned for a second spell when Mancini was appointed manager.
Revenge: Manchester United fans have put up a billboard poking fun at their rivals and former player in Piccadilly Gardens, aping the infamous 'Welcome to Manchester' sign displayed by City after signing Tevez
Mancini's agent Maurizio di Giorges, who represents the entire family, said: 'I didn't know that he refused to come on. At this moment I am looking to find clubs for both of them.
'I don't know what the future is, but they need to be away from the shadow of their father.
'They train with the Elite Development Squad but the opportunities are limited at a club like City.'
Next test: City are preparing to travel to Blackburn this weekend
QPR manager Neil Warnock weighed into the Tevez controversy, saying: 'The sooner he leaves the country, the better. Within a few months he'll be kissing another badge.'
Warnock has no love for Tevez, who was at the centre of the third-party ownership saga four years ago that saw West Ham keep their Premier League status at the expense of Warnock's Sheffield United.
All the rage: QPR boss Neil Warnock has blasted Tevez's actions
The QPR manager called on FIFA to act, saying: 'The top authorities like FIFA have got to come up with something because, quite honestly, two weeks' ban is a disgrace for an offence like that.
'You should be banned until January because a manager has no option but to say that you won't play for the club again. You can't do that because the PFA would cry foul on that and get all the solicitors involved. So FIFA have to come up with an answer.'
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