The deal, which excludes a purchase clause, is being finalised amid negotiations over salary arrangements.
Arsenal are expected to cover part of Vieira’s wages, with the player agreeing to a pay cut to make the move happen.
Vieira, who joined Arsenal for €35 million in 2022, struggled to secure a consistent role under Mikel Arteta, with injuries hampering his progress.
His reported excitement for the potential return to his boyhood club is shared by Porto fans, who are eager to see him back in blue and white.
The discussions highlight Porto’s financial limitations, as the club cannot afford Vieira’s full wages, reportedly around €1.5 million annually.
Vieira’s willingness to accept a reduced salary underscores his desire to return to playing regularly, hoping to rediscover his best form after a challenging period in London.
Arsenal’s midfield is set to become even more crowded with the imminent arrival of Mikel Merino, further reducing Vieira’s chances of regular minutes.
This prompted the move, as the midfielder looks for a fresh start in a familiar setting.
The deal is expected to be finalised soon, with Vieira ready to travel to Porto to complete formalities.