Saliba played a key role as France reached the semi-finals of the tournament before returning to London this week, where specialist assessments identified the issue. Arsenal have since released a full statement on the defender's condition and the recovery plan now in place.
The statement read: "William Saliba has returned to us from World Cup duty, where he played an integral role in France reaching the semi-finals of the competition.
"Subsequent specialist reviews on William's return to London this week have confirmed that he has suffered a back injury which will require a period of rehabilitation.
"Extensive assessments have concluded that surgery is not recommended, but William should now commence a managed recovery programme.
"William's rehabilitation will commence immediately, with continual management of his injury, and he is expected to be out of action for an extended period.
"Everyone is fully focused on supporting William to ensure he is back to full fitness as soon as possible."
The club have not put a specific timeframe on his return, and the injury leaves Arsenal needing to reassess their centre-back options as they continue preparations for the new season, with Saliba having been first-choice alongside Gabriel Magalhaes.
Cristhian Mosquera, or Piero Hincapie, are the most likely candidates to deputise in his absence, with Arsenal having moved on fellow defender Jakub Kiwior last summer, leaving a leaner group of centre-back options heading into the new campaign.
The 25-year-old's setback also comes at a sensitive time in his contract situation, with the defender previously linked with a move to Real Madrid amid ongoing talks over fresh terms at the Emirates Stadium.
Arsenal will be keen to avoid those uncertainties being compounded by a lengthy spell on the sidelines, particularly with the club aiming to build on last season's title challenge under Mikel Arteta. Further updates on his recovery timeline are expected in the coming weeks as his rehabilitation progresses.