The Greece Under-21s international will become the Gunners' first signing of the winter window, likely within the next 48 hours once the finishing touches are made.
Arsenal boss Wenger revealed after his side's 2-2 draw with Chelsea on Wednesday night that the young centre-back will first undergo a medical, before then being sent out on loan to gain further experience.
"He's not ready to play for us," the Frenchman told reporters. "We'll give him out on loan."
Bundesliga side Werder Bremen are expected to snap up Mavropanos for the second half of the campaign.