The club, which recently gained promotion to the English top-flight, is moving quickly in the transfer window to strengthen its squad.
After adding Habib Diarra from Strasbourg, Sunderland is now reportedly close to signing Reinildo, a 31-year-old left-back.
According to reports, Reinildo will sign a two-year deal with the club, bringing experience and depth to the team.
During his three-year stint with Atletico Madrid, Reinildo made 103 appearances in various competitions, mostly as a backup player.
