The 25-year-old midfielder, who was born in Belgium and grew up in Europe, will return to his father's country of birth and the international team he represents for the first time in his professional career.
Pereira joins Flamengo on a season-long loan.
United will be hoping Pereira can kick on and increase his resale value during his time at Flamengo so that they can part ways on a permanent basis next year.
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