A hedgehog "blown up like a beach ball" has been rescued and diagnosed with a severe case of balloon syndrome.
The animal, which had inflated to twice its size, was spotted wandering around in circles by a member of the public in Toll Bar, Doncaster.
RSPCA inspector Sandra Dransfield said it was clear the animal was suffering the rare condition, which is caused by gas collecting under the skin.
The male hedgehog is being treated at an RSPCA centre in Cheshire.
Ms Dransfield said: "It's the worst case of balloon syndrome I've seen.
"This poor chap was almost twice its natural size, literally blown up like a beach ball with incredibly taut skin.
"I took the stricken animal straight to Peak Vets in Sheffield, where he was X-rayed and they released some of the air from under his skin.
"The vet then started him on a course of antibiotics and pain relief. We found him in the nick of time, and I really do hope he pulls through."
An RSPCA spokesperson said balloon syndrome can be caused by a traumatic event, like an injury, or underlying infection, which releases gas into the cavity under the hedgehog's skin.
Treatment requires the skin to be punctured and a course of medication.
The large 1kg (2.2lb) hedgehog has been transferred to the RSPCA's Stapeley Grange Wildlife Centre in Nantwich, Cheshire, where he will be thoroughly examined under general anaesthetic and more air released.
He will be cared for at the centre until he is ready to be returned to the wild.