Ernie Gordon, 75, of Alnwick, had to go to the town's infirmary to have a tetanus injection and be put on antibiotics after his altercation with the creature, named Elvis.
Ernie, who penned the book The Adventures of Rusty Red Coat Volume 1, was called out to rescue the squirrel after reports that it was injured.
He took him to Alnorthumbria Vets in Alnwick where X-rays revealed that Elvis had fractured its pelvis.
Ernie said: "The vets were absolutely great and when I found out that he had a fractured pelvis I knew straight away that I had to call him Elvis."
Retired Ernie took Elvis home to recover. But when he was moving him into a make-shift intensive care unit – a lawn mower box, with wire caging and filled with straw – Elvis struck.
Ernie said: "He locked onto my thumb and then my index finger. There was blood everywhere. There was some power in those jaws, I can tell you!"
After a lot of persuading Elvis eventually let go.
Ernie is planning to gradually reintroduce the squirrel to local woods before eventually releasing him back to the wild.