De Jong was attempting a move on Gasly during Saturday's feature race, but the pair rubbed wheels and collided, sending De Jong into the tyre wall at high speed.
He was transferred by helicopter to hospital in Liege where doctors confirmed he had suffered a fractured vertebra, and he underwent a successful four-hour surgery on Saturday night.
Gasly admitted after the race that he didn't leave de Jong enough room because he wasn't expecting him to be on the outside.
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"To be fair I wasn't looking in the mirror, I was already looking at Blanchimont and I didn't leave him enough space," said Gasly.
"When I saw the footage again from the inside of the car it's always different, especially at that speed in that corner.
"It was a big one and it could have been much worse.
"I have to say I am sorry for him. Hopefully he can be back in the car soon."
Gasly was penalised for the incident with a 10-second time penalty.
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".
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