A devastated mum has questioned how heartless thugs could have bashed her son and left him for dead in Whittlesea last August.

Hamish Layton, 44, was walking in the township with his dog on August 20 when he was hit in the back of the head by an unknown offender.

Mr Layton was found in a pool of blood by a passerby at the intersection of Church and Fir streets about 11.30pm.

He was conscious but had suffered serious head and spinal injuries.

Mum Joan Sparkes said the assault had left her son paralysed and confined to a wheelchair.

He is only able to use one arm and has an acquired brain injury, affecting his memory of the attack. His injuries are so severe that Mr Layton receives around the clock high-quality care and will likely end up in a nursing home.

“It’s devastated me … it’s consumed me if you like,” Ms Sparkes said.

“How can you leave someone on the street to die? If someone hadn’t found him, he’d be dead.”

Ms Sparkes said the assault had affected the entire family, including her son’s three adult children.

“I can’t tell you how it has affected me … I feel so useless,” she said.

Last Monday, police set up an information caravan in Fir Street in search of more information. They believe that more than one person may have been involved in the assault.

Acting Detective Senior Sergeant Christine Lalor said police did not know where Mr Layton was attacked, who attacked him or why.

“It is devastating injuries and it is terrible what’s happened,” she said.

“For someone to assault someone and cause those sort of injuries is devastating.

“We believe that there are a number of people either involved or who have information that may assist police.”

Anyone with information about the assault is urged to contact Crime Stoppers on 1800 333 000 or crimestoppersvic.com.au