The 26-year-old Mari arrived to London on Saturday, where he will be on the verge of joining the Premier League side. Mari had a release clause of €30 million euros but the clubs have agreed to €10m, according to sources.
Mari has been with the Brazilian giants since July 2019, and was instrumental in the Rubro-Negro winning the domestic and Copa Libertadores crowns.
He also featured for Flamengo in their run at the Club World Cup, where they lost to European champions Liverpool in added extra time.
Mari, who was on Manchester City's books from 2016-2019, was previously at Deportivo La Coruna before his stint in Brazil. Despite never playing a single match at the Etihad, Mari is said to be close with Arsenal manager and ex-City assistant Mikel Arteta.