The family of missing 87-year-old Ballan man Brian Andrews hold grave fears for his safety and are appealing to the public for any information on his whereabouts.
Mr Andrews, who lives alone, is normally in daily contact with his son.
He was last seen at his Inglis Street address about 1pm on December 7. He left his home in a distinct grey Citroen with with a maroon roof, registration IBE 9GJ.
Mr Andrews' son Peter said it was "really unusual" for his father to go missing and that he hadn't gone away "in the last four years".
He said his father can occasionally appear "slightly disoriented".
"When he is in unfamiliar territory and not sure where he is, he will definitely be a bit confused and disorientated," Peter said.
"He is very sociable and will always talk to people."
Leading Senior Constable Kenneth Birch said police have concerns given Mr Andrews had been missing for a number of days.
"There are a lot of ongoing investigations [into the disappearance] happening at a local level in Ballan," he said.
Constable Birch said that Mr Andrews spoke to family members regularly and is known by a number of residents in the small Victorian town.
He said it was "very out of character" for the Ballan local to disappear without contacting a loved one.
"Every day he has contact with his son," he said.
"He has left with a sum of cash and we are investigating in relation to that and we still have ongoing inquiries."
Peter said his father is generally healthy but is currently on medication to help him maintain a normal body temperature.
"He has a pacemaker and the medication he is on is to regulate his body temperature," he said.
"He hasn't taken [his medication] for a few days and may appear a bit hot and sweaty. With the weather getting warmer it could land up being quite serious."