On debut in Canterbury's 18-6 loss to Cronulla, the 22-year-old centre knocked himself out attempting to tackle veteran Andrew Fifita in wet conditions.
Play stopped for close to five minutes while Casey lay on the ground and after leaving the field in a medi-cab, he was admitted to Westmead Hospital where he underwent CT scans.
Casey was released from hospital that night and could return to the Bulldogs line-up as soon as round 18, when the side plays its next game against South Sydney.
"Declan Casey was cleared for any spinal injury after a precautionary check up at the hospital post match," the Bulldogs said.
"He will undertake mandatory concussion protocols to return to play."
Casey struggled to adapt to the wet conditions on debut but could yet have another chance to prove himself as Corey Allan, the man he replaced in the starting side, will be sidelined for around a month with a groin injury.
Barnstorming forward Tevita Pangai will miss the Rabbitohs game after rupturing a muscle near his Achilles tendon in the loss to Cronulla.
He is on track to return the following week against Gold Coast.
"Scans showed a rupture to the plantaris tendon which lies adjacent to the achilles," the Bulldogs said.
"Pangai Junior will resume running when pain settles."
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