Dubbed the 'Brazilian Paul Pogba', the 18-year-old will join City on a five-year contract after the two clubs agreed a deal, per The Sun.
City will send out Metinho on loan immediately, with French club Troyes touted as an option.
The French club are part of City's sister group.
Metinho is viewed as one of Brazil's brightest young talents, having captained Fluminense's Under-17s to Brasileirao trophy glory and the Copa do Brasil final in 2020.
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