The French captain, 33, played 45 minutes during the devasting 5-0 defeat to Derby County on Monday evening.
Koscielny has been unavailable since he suffered a serious Achilles injury during a clash against Atletico Madrid in May.
The defender gave the Gunners a huge boost when he was spotted training with his team-mates last month.
And he was named in Freddie Ljungerg's starting line-up for the Premier League 2 clash against the Rams.
Arsenal were 1-0 down at half-time when the 33-year-old was replaced by Jordi Osei-Tutu.
Without the first-team skipper on the pitch, the Gunners let in four goals and lost the game 5-0.
Koscielny's replacement lasted just 10 minutes before he was shown a red card following an altercation with George Thorne.
Gunners youngster Daniel Ballard also received his marching orders in the second half for a reckless challenge.
Unai Emery hinted earlier this week that the French star is close to making his highly anticipated return to the senior squad.
He said: "He is looking well, with good performance, good feeling and I think he, today, is close to also playing with us."
The Gunners have managed to cope without their captain and are unbeaten in their last 17 games in all competitions.
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