NSW police seek help in finding basher

A man punched in an apparently unprovoked attack on the NSW Central Coast remains in hospital with life-threatening injuries, as police appeal for help to find his attacker.

Police say Graeme Wilton was on holiday with his wife at Mannering Park on December 12 when he was attacked while on his daily walk.

Witnesses told police they saw a white utility stop near Mr Wilton and the driver get out and punch him in the head, causing the 56-year-old to fall to the ground unconscious.

Mr Wilton is in Royal North Shore Hospital life-threatening head injuries.

Tuggerah Lakes Local Area Command crime manager Detective Inspector David Waddell said on Monday police believed the attack was unprovoked.

"His family is distressed and are at a loss as to why anyone would do this to Graeme," he said.

Det Insp Waddell said police were urging witnesses to come forward to help clarify the circumstances of the assault and find the offender.

Investigators have released an image of the man they are seeking.

He is described as being of Caucasian appearance, aged in his 20s or early 30s, about 183 centimetres tall, with short dark hair.