He was taken to a veterinary specialist Monday after a wanted parolee threw him out of a second-story window on Sunday.
Jaris suffered a large gash to his head and was staggering before he was taken to a hospital.
Police said they're awaiting tests to determine if he suffered brain damage.
"This is a first," said Lt. Gary Aulis, head of the department's K-9 program. "Of the dogs injured in the line of duty, we've never had something even remotely like this happen. "
On Sunday, police came to the 9500 block of Mango Avenue about 12:30 p.m. in search of Bryan Bills, 28, of Fontana, who was listed as an armed and dangerous parolee.
A woman answered the door and said that no one else was in the house, but then officers heard noises coming from the second floor of the residence.
An officer standing outside saw Bills trying to climb out of an upstairs window.
He refused to surrender to officers, so police sent their dog, Jaris, into the home.
When Jaris ran toward Bills, Bills used the dog's momentum to throw the animal out of an open window. The dog fell on his head on the concrete below, police said.
Bills was arrested on suspicion of injuring a police dog, resisting an officer and violating parole. He was booked into West Valley Detention Center in Rancho Cucamonga.
Jaris, who has worked for Fontana Police Department since 2008, has suffered minor bumps and bruises on the job - either from being struck by suspects or during searches.
"Most suspects can't just sit there when they're being bit by a dog," Aulis said. "They hit, kick, pull, whatever they can do to get the dog off of them. "
Now, the department is forced to wait and see whether Jaris will recover from the incident.
Aulis said the department is focused on the animal's health first, but he hopes to eventually return Jaris to duty if he is given a clean bill of health.
"Apparently it's very difficult to diagnose neurological injuries with a dog," said Fontana police Sgt. Robert Morris.