The centre-back has spent the season on loan at Marseille, and reports in France claimed the 21-year-old hoped to stay on with the Ligue 1 club for another campaign.
However, Arteta says he will need Saliba in 2022-2023 as Arsenal faces Europa League commitments alongside its Premier League duties, and it means a long-awaited competitive senior debut awaits the young defender.
The France international was signed by Arsenal from Saint-Etienne in July 2019, but immediately loaned back to Les Verts, and subsequent loans with Nice and Marseille have followed.
Saliba was a near ever-present for Marseille, which finished second in Ligue 1, and was named in the league's team of the season.
He won his first two senior caps for France in March friendlies against Ivory Coast and South Africa, putting him in the frame for a World Cup place. He has also been included in Les Bleus' squad for next month's Nations League games.
"He has to come back," Arteta said. "He has the experience and the environment necessary to be competitive with us.
"If he had stayed with us this year, with one Premier League match per week, with Ben White and Gabriel, he wouldn't have had half the playing time he had with Marseille, that's for sure.
"For his growth and what he can do next season that wouldn't have been good. William wasn't with us because he wouldn't have had the playing time to gain experience. That's it, there's nothing else."