Santos arrived in Brazil earlier today to complete negotiations with Gremio and sign a loan deal for the rest of the season.
The 29-year-old has fallen behind Kieran Gibbs in the pecking order in his second season at the Emirates Stadium and saw his position in the squad weakened by the signing of Nacho Monreal from Malaga last month.
In a short interview, Santos revealed that his desperation to play first-team football has resulted in a move back to Brazil.
He told Radio Bandeirantes: "I've come to Gremio to become champions. I've very excited about this project.
"I now need to play for match fitness. With five or six games I will be better physically."
Santos has featured just eight times in the Premier League for Arsenal this season.