The 20-year-old Japanese international was loaned out to the Dutch side shortly after joining the Gunners in 2011.
"It's right we are also working on Ryo Miyaichi, but at the moment it's not clear what the situation is," Koeman told NuSport. "After that, we can make a step. It's not that far yet."
Miyaichi has also enjoyed loan spells with Bolton Wanderers and Wigan Athletic during his two years in English football.