The left-back has been back in his homeland for the past few months after joining Gremio on loan in February, following a difficult period at Emirates Stadium when he fell down the pecking order and was criticised for some of his performances.
He is now set to seal a permanent switch to Flamengo, with reports suggesting that he will sign a contract with the club until 2015.
Flamengo had been facing a nervous wait to finalise the move ahead of the Brazilian transfer deadline on July 20, but a deal has now been agreed and is close to being rubberstamped.
"The Arsenal document we were waiting has come," Flamengo's director of football Paulo Pelaipe told UOL.
"Everything is agreed between the player and the club. We are just waiting for the document that authorises the transfer to announce him, it should come by Friday.
"Andre Santos is already at the club's hotel for the medical."
Santos has also expressed his joy at the imminent switch and hopes to play his part in a successful period for Flamengo.
"The feeling couldn't be better, as I am very happy with the achievement of playing for a great club like Flamengo," he is quoted as telling Globo Esporte.
"I feel like a winner. I hope to make history here, be champions and help Flamengo win many games and titles."