"Head of a Man," currently on loan to a gallery in Scotland, has been labeled a forgery by the director of ArtWatchUK, Michael Daley, the Australian reports.
Daley's pronouncement was published in the Sunday Times of London along with the comments of other British academics and art critics.
"It isn't convincing as a work by Van Gogh's brush at that date, but whoever did it was a talented person," art historian and Van Gogh biographer Tim Hilton says.
The Times' art critic, Frank Whitford, who saw the work in Scotland recently, said it was clear to him it isn't a Van Gogh.
Painted in the late 1880s, "Head of a Man" was purchased in 1940 by the National Gallery of Victoria for about $200,000.
If it is authentic, its value could be as high as $20 million.
Interpol investigating stolen passports on missing flight
Teacher apologizes for showing sexual image of herself in class