The centre-back joined the Gunners in the January transfer window on loan from Brazilian top-flight side Flamengo, with the report adding that Arsenal paid a loan fee of €5m (£4.2m) for the 26-year-old.
Coluna Do Fla claim that the total permanent deal for the defender is worth up to €16m (£14m) – when taking into account bonuses and other fees.
Mari was sidelined with an ankle injury in the opening quarter of Arsenal’s clash against Manchester City during midweek, with the Sun reporting that the ace will be out for the rest of the season.
Mari has only made three appearances for the north London outfit, he’d just seemed to establish himself as a starter under Mikel Arteta when the injury hit.
Arteta clearly sees something in Mari, the Gunners are in need of younger centre-back options considering the likes of David Luiz and Sokratis are approaching the final years of their careers.
The Spaniard could be a fine partner for French wonderkid William Saliba, who was signed last summer for big-money and will be available for the first-team as soon as next season starts.
It looked as though Arteta had steadied Arsenal’s notoriously shaky defence after being appointed as boss, but Wednesday’s performance against City highlighted that the Gunners are still far too lacklustre at the back because of the frequency of costly individual errors.