Currently on loan in Scotland, the work, "Portrait of a Man" or "Head of a Man", has been questioned because of deviations from Van Gogh's accepted style.
But despite the controversy, Victorian National Gallery director Gerard Vaughan believes the work is genuine.
"I would be very surprised if it were proved to be a forgery," Mr Vaughan said.
"Nearly every scholar who has published on (Van Gogh) through the 20th century has accepted the authenticity of the Melbourne picture."
The work came under scrutiny after being shown at the Dean Gallery in Edinburgh.
Sceptics have pointed out it is the only horizontal portrait by Van Gogh, is not mentioned in any letters by the Dutch master, is mounted in a manner unusual for Van Gogh and appears to have had the lower part, where a signature could have been, removed.
Mr Vaughan said he wanted the truth about the painting to be known. "We welcome debate, we welcome inquiry and what we'll be doing now is beginning a project," he said.
"We'll be talking as quickly as we can to the Van Gogh Museum in Amsterdam, we'll be talking to a number of other leading Van Gogh scholars, and we'll see where (we) get to.
"At the end of the day, we stand for scholarship and we stand for truth, and so whatever the overwhelming consensus of scholars might be in relation to this picture, we'll take very serious note of it."
If the painting is an authentic Van Gogh, it would be worth about $25 million, but would be almost worthless as a fake.