The wife of a missing Melbourne academic says she is "totally scared" by his unexplained disappearance and fears he may have become lost while walking in bushland in Melbourne's north-east.

A large-scale search is under way to find Professor John Forster who has not been seen since the weekend.

Professor Forster was last seen at his house in James Cook Drive in Diamond Creek in Melbourne's northeast about 10am on Saturday.

Police found Professor Forster's green Subaru Forester station wagon at the car park at Sugarloaf Reservoir in Christmas Hills, about 20 kilometres from his home, on 11pm that day.