League Two Crewe Alexandra signed the academy product on loan for the season.
Okonkwo, 21, is the first to go - yet he is the one who the Gunners believe can eventually make a first-team breakthrough.
Selling the Londoner this transfer window was out of the question.
Instead the Gunners "look forward to seeing his continued development" with Crewe rather than in Under-23s football.
Okonkwo made the Arsenal matchday squad seven times but has yet to make a senior appearance.
His temporary exit leaves Gunners' U21 aces Karl Hein and James Hillson competing for promotion to the first-team squad.