De Jong, who was described as being conscious and in good spirits after the crash, was transferred by helicopter to hospital in Liege for further assessment following the race.
Doctors there confirmed the Dutchman had fractured his sixth vertebrae and that it needed immediate attention.
AUTOSPORT understands de Jong underwent a successful four-hour surgery last night.
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He is in now in a stable condition, but will remain in Liege hospital next week.
The GP2 series issued the following statement from de Jong's family: "We would like to thank the medical team that treated him with success and would also like to thank their colleagues, the GP2 drivers and teams and the series organisers for their support."
The accident happened when de Jong and Gasly ran side by side through Blanchimont early in the race.
The pair rubbed wheels and collided, the contact sending de Jong hurtling towards the barrier on the outside at speed.
On impact the MP Dallara was engulfed by and rode up the tyre wall, which caused the race to be red-flagged as medical staff carefully extracted de Jong from the awkward position.
DAMS driver Gasly was penalised for the incident with a 10-second addition to his Saturday race time.
According to a GP2 statement, the stewards ruled that Gasly "moved to the right of the track colliding with de Jong. The latter had a significant portion of the car alongside Gasly."
That punishment was in addition to a 30s penalty for being one of a group of drivers judged to have failed to slow down sufficiently during the safety car period for the crash.
Richie Stanaway, Marlon Stockinger, Sean Gelael and Nick Yelloly were also penalised for this infringement, getting 30s time additions in lieu for 10s stop/go penalties in the race.
As Yelloly retired following a collision with Nobuharu Matsushita, his penalty becomes a pitlane start for Sunday morning's race instead.
Stockinger was the only one of the penalised drivers to have finished in the points, taking 10th, and his demotion to 17th means Gustav Malja scores on his GP2 debut.
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