York Regional Police say that a homeowner saw a dog curled up under a tree and called authorities last Sunday.
The responding officer, Const. Netashia McLellan, said it was immediately apparent the dog was in distress.
"He was curled up under a tree, he wasn’t doing very well. I think every breath was a struggle for him," McLellan told reporters on Thursday morning.
The Ontario SPCA was notified and the dog was taken for treatment at an emergency veterinary clinic in Richmond Hill, Ont.
It was subsequently determined that the head injury has left the dog blind in one eye.
The dog also has the number “191” branded on both sides of its body.
While McLellan said the dog has seen a "big improvement" since being taken for treatment, it is still unclear where the animal came from and who is responsible for the branding.
Anyone with information is asked to contact OSPCA investigators.
Click on the video above to see a full report from the CBC's Lucy Lopez.