The 28-year-old woman was running through Lal Lal State Forest, near Ballarat, west of Melbourne, about 4.30pm on Saturday when she was attacked near the Blast Furnace Picnic Area.
Police said she was approached by a man who hit her in the head with a “handmade weapon with a rock attached”, knocking her unconscious.
She woke to find the man had gone.
After running 4km back to her car, she contacted police and was taken to hospital with non-life-threatening facial injuries.
Austin revealed the extent of her injuries on social media, telling her followers she “is home but in shock” with a “massive throbbing headache”.
Detective Senior Sergeant Tony Coxall described the attack as very “serious”.
“We have not found the weapon,” he said.
“We will be upping out patrols in the area, it’s the only incident we have reported in the area.”
Coxall however said appeared to be a “one-off” attack.
Her attacker has been described as Caucasian in appearance and as having been wearing black jeans, a cap and no shoes or shirt.
Anyone who witnessed the incident or who has information is urged to contact police.