William Saliba played a full 90 for Arsenal U23 on Friday night.
Saliba played 90 minutes for the club's U23 side as they drew 2-2 with Brighton on Friday evening.
Saliba signed for the Gunners a year ago but was immediately sent back on loan to St Etienne in France for the 2019/20 season.
He joined up with his new colleagues in preseason, but, having bolstered his centre-back options with the signing of Gabriel Magalhaes from Lille, Mikel Arteta has decided to take his time easing Saliba into the first team picture and he was not named in the matchday squad for last weekend's Premier League win over Fulham.
"I think it's going to take him [Saliba] some time to adapt to our way of playing but as well to get adapted to the language, the rhythm, the physicality of the country," Arteta said last week.
His U23 appearance means he is highly unlikely to be involved in Saturday evening's home clash with West Ham.
Goals from Ben Cottrell and Folrain Balogun had seen Arsenal come from behind to lead the Seagulls after Teddy Jenks' penalty had opened the scoring, but Danny Cashman struck on 73 minutes to earn a share of the points.