The 19-year-old winger is flying to Germany to complete the season-long loan, as per Sky Sports.
Mikel Arteta and Arsenal are keen for Nwaneri to gain more regular minutes, which will be hard to come by in the Gunners' current set-up.
Nwaneri made six Premier League appearances for the Gunners last season before joining Marseille on loan, compared to 26 the previous season, when he netted four times and provided two assists in the English top flight.
The Englishman is set to play his football at the Signal Iduna Park this season under manager Niko Kovac.