The Frenchman signed for the Gunners in the summer, but a season-long loan back to the Ligue 1 outfit was a non-negotiable part of the deal, with the player believed to have wanted another year of development in his homeland.
As a result, Arsenal were forced to sign David Luiz from Chelsea on deadline day to add to their defensive options.
However, Saliba has not yet played in France this season as he has struggled with an adductor injury.
The youngster has therefore flown to London Colney so that Arsenal can manage his recovery, hoping to return to action soon and continue his development this season.
In the meantime, the Gunners must rely on Sokratis, Calum Chambers and Rob Holding, who appears to be nearing a return from his own injury, while Shkodran Mustafi seems to have been frozen out of the first-team picture.