The incident happened early Wednesday morning.
Surveillance video shared by the University Veterinary Center shows the dog inside a plastic bag being tossed over a fence, landing into the backyard area of the clinic.
The dog was found seriously injured by the veterinarian the following morning.
"I can't find words to describe why anybody would do something like that, and it's hard to find the right words," Dr. Ash Hakhamian said. "I mean, thrown is an understatement. He sustained mental trauma, even far beyond his physical trauma."
Hakhamian was surprised when he discovered the dog in the back of his clinic. At first, he didn't know how the dog ended up there.
"We decided to review the security camera footage, and to our disappointment we found the pet was placed there by being thrown over the fence," he told ABC .
"He face-planted," Hakhamian added. "That's what broke his fall, was his face."
In addition to the trauma and severe bruising, Hakhamian says the dog is severely anemic, malnourished and was covered in fleas.
"His nails are so long, they have curled and gone back into his paw," Hakhamian said. "That's a type of neglect that proceeds this trauma, it proceeds this abuse."
The clinic said that due to the nature of the situation, the Anaheim Police Department and Orange County Animal Care are now involved and that the dog is "receiving around the clock care to ensure he is recovering from both his injuries and ongoing medical needs."
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While he's expected to fully recover, the dog remains in critical condition.
After reviewing the surveillance video, the veterinarian's office thought the woman responsible came from the apartment building across the street.
Police confirmed that's where she was found earlier on Thursday.
The Anaheim Police Department said the woman seen in the video has not been arrested, but police are discussing the case with the Orange County District Attorney's Office to see if it qualifies for criminal charges.
Officer Breana Castro with Anaheim police said the woman has spoken with detectives.
"Her statement was taken, and it is going to be presented to the district attorney's office for charges," Castro said.
The dog is not currently available for adoption.
"There is going to be a lot of medical care and other things involved before he is going to be made available to the public for adoption and/or foster care," a statement from the clinic said.
The incident remains under investigation.