Atletico Mineiro have agreed to terms with Real Madrid to sign the 23-year-old Brazilian player.
As part of the deal, Real Madrid will release Reinier for free, but they will retain a 50% resale clause.
Reinier joined Real Madrid from Flamengo in January 2020, but he never played a competitive game for the Spanish club.
Instead, Reinier was loaned to several teams, including Borussia Dortmund, Girona, Frosinone, and most recently Granada.