A young man with critical head injuries may have been bashed with a skateboard while walking through parkland in Sydney's northwest.
He was attacked near Macquarie University, on Culloden Road at Marsfield, shortly after 2am (AEST) today.
"The person has allegedly been hit and ... he has fallen backwards," A NSW Ambulance Service spokesman told AAP today.
Paramedics arrived to find him unconscious with what appeared to be a closed head injury.
Police are investigating reports he was hit in the head with a skateboard.
Described only as a male aged in his late teens to early 20s, he was in a critical condition when admitted to the Royal North Shore Hospital.
Police say a 21-year-old man is assisting with their inquiries.