Gunners boss Mikel Arteta wants the 21-cap Brazil international to add competition for places in midfield for the rest of the season.
But while the player has agreed to the switch, his club won’t release him until they sign a replacement.
And Arsenal, who will pay a small loan fee for the 25-year-old and cover his wages in full, are ready to play a waiting game to get their man.
The Gunners need cover now as Thomas Partey and Mo Elneny are both away at the Africa Cup of Nations.
But Arteta, who is unlikely to spend big money in this window, sees Arthur as a player who can make impact even after they return, and is prepared to be patient.
While he is under contract until 2025, his long-term future there is in doubt.
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Meanwhile, Gunners defender Pablo Marí is expected to complete a loan move to Udinese in the next few days.
Arsenal are also expected to keep tabs on a new striker this window.
Both Alexandre Lacazette and Eddie Nketiah are out of contract in the summer, while the future of Pierre-Emerick Aubameyang remains up in the air.