[5] On 9 November 2019, Reinier extended his contract with Flamengo until 31 October 2024 with a release clause set at €35 million.

[6][7] On 20 January 2020, Real Madrid CF announced that the club reached an agreement with Flamengo for the transfer of Reinier, who signed a contract until June 2026.

[17] On 1 September 2023, Reinier agreed on a loan deal to newly-promoted Italian Serie A club Frosinone until the end of the 2023–24 season.

On 7 March 2018, Brazil U17 manager Paulo Victor Gomes called up Reinier for the Montaigu Tournament in France.

[23] He captained Brazil for the 2019 South American U-17 Championship in Peru and started all four group stage matches, scoring three goals.