The 26-year-old is in London with Arsenal technical director Edu, who is helping to negotiate the deal with the Brazilian club.
Mari has even done his medical, but the clubs have not agreed on a fee.
Brazilian reports suggest that Arsenal want a loan to the end of the season with an option to buy.
ESPN Brazil suggests that Mori is desperate to play in England and wants the deal concluded.
But Flamengo will not accept anything but a direct transfer or a loan with a guarantee of a purchase.
They do not want an option to buy, as it means they could be saddled with the player after the Premier League season ends.
Another source, Coluna do Fla, suggests the deal is close to being concluded.