Saliba, signed in 2019 from Saint-Etienne for a reported fee of about £27 million ($37 million), has yet to play for the senior team.
As part of the deal, he returned to Saint-Etienne for a season on loan while he also had a six-month loan spell with Nice last season.
“Together with William, we have decided it will be good for his continued development to spend another season on loan,” Arsenal technical director Edu said in a statement.
“William joined us as an 18-year-old, and he is still only 20, so he is still developing all the time.”
Arsenal’s William Saliba joins Marseille on loan
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