The animal, inflated to twice his size, was wandering around in circles in Toll Bar, Doncaster, when it was spotted by a concerned member of the public.
She told the RSPCA last Monday that the hedgehog was dragging its back leg, had blood on its nose and due to its size might be pregnant.
But when RSPCA Inspector Sandra Dransfield arrived, she could see that the animal was suffering from the rare condition balloon syndrome, when gas collects under the skin of the hedgehog, so it inflates like a balloon.
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."
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.
The large 1kg hedgehog has been transferred to the RSPCA's Stapeley Grange Wildlife Centre in Nantwich, Cheshire.
He will be put under a general anaesthetic to be thoroughly examined and more air released.
He will continue to be treated at the centre for this unusual condition and cared for until he is ready to be returned to the wild.
If you see an animal you have concerns about, the RSPCA urges you to call its emergency line on 0300 123 9999.