Mari was filmed arriving at London Heathrow airport with Arsenal's technical director Edu.
It's believed that he was due to undergo a medical over the weekend ahead of completing a move to the Gunners.
Mari spent three years at City but didn't play a single game and, after three consecutive loan spells, he joined Flamengo last year.
It's reported that Mari may have even completed the medical that he was booked in for, before boarding a plane back to Rio.
The 26-year-old will be hoping the deal is concluded soon as he even had friends congratulating him and wishing him well for his move on social media.
Arteta leads Arsenal into their FA Cup fourth-round tie against Bournemouth this evening.
How are the Premier League's top sides doing in the January transfer window?
The numbers don't show it, but Arsenal are a different side under Mikel Arteta
