Over the weekend, it was suggested that a deal was close to completion, with Mari having travelled to England to finalise the transfer.
However, according to an unnamed Flamengo director, that is no longer the case due to Arsenal allegedly wanting to make changes to the previous agreement.
The club official is quoted by the Daily Mail as saying: "We expect him at Ninho do Urubu this afternoon. We had agreed to sell him for a fee, he arrived in London, Arsenal changed the terms. Flamengo is a serious club."
Flamengo are due to begin pre-season training this week ahead of their upcoming domestic campaign.
Mari, who has a contract until 2022, made 30 appearances last season, helping the club to the Copa Libertadores and the final of the Club World Cup.