The bombshell announcement about the El Coloso (Colossus), a large-size work depicting the torso of a giant bursting through the clouds as he marches above a terrified village, is causing a furor among the art world.
Many experts are upset at how the Prado has handled the matter and at least one still insists the painting was done by the 18th century master.
Francisco de Goya y Lucientes' Colossus has always been one of the Prado's major attractions and a highlight of his series on Spain's war against Napoleon, whose troops invaded in 1808.
Doubts about the work's authenticity began to surface in the early 1990s, but eyebrows were raised in April when the museum unexpectedly excluded the painting from its blockbuster show "Goya in Times of War."
Then the museum finally announced last week that it no longer considered the painting a genuine Goya.
On Friday, the controversy flared anew in the pages of Spanish newspapers.
"I'm tremendously skeptical," Zaragoza Art History Professor and Goya expert Arturo Anson told leading daily El Pais, arguing that a more extensive debate must be held.
The Prado, meanwhile, says despite the decision, there are no plans to move the Colossus from its position in the Goya rooms.
The museum says fresh studies indicate the Colossus may be the work of a minor painter, Asensio Julia, a pupil and a workshop assistant of Goya's. One of the most significant findings, it says, are what appear to be Julia's initials at the bottom of the painting.
"The museum is certain it is not a Goya. That's for sure. What's not so clear is who actually painted it," a Prado spokeswoman told The Associated Press. She spoke on condition of anonymity in keeping with museum policy.
The Prado, which holds the world's biggest collection of Goyas and considers itself the leading authority on the artist, says an investigation into who actually painted the Colossus is not expected to wind up before the end of this year.
Manuela Mena, a Goya expert and the Prado's chief 18th century art conservationist, told a news conference recently the painting is filled with stylistic points that don't match Goya's talent.
The giant's raised left arm is too crudely painted for such an anatomy expert as Goya, she said, and his expertise in drawing bulls and other animals was far greater than what appears on this canvas.
"The painting is not by Goya's hand," El Pais quoted her as saying. "Goya would never have painted it like that."
Others disagree.
Nigel Glendinning, a leading British art historian and Goya expert, told The Associated Press in a telephone interview from London that he still believes the painting is genuine.
He said the Prado should have published a scholarly paper laying out its argument, rather than announcing its findings as fact in the press. Glendinning dismissed Mena's argument about the crude style of Colossus, saying Goya often preferred broad, rough brush strokes.
"I think it's a Goya," he said.
Glendinning pointed to other evidence as well, including written records. He says a work by the same name was in Goya's house in 1812. The painting, he maintains, turned up in the inventory of an aristocratic family in Madrid in 1874, and one of their descendants turned it over to the Prado in 1930.
While the Prado's decision to reclassify the painting represents one of the biggest attribution changes ever for the museum, few believe it will effect the painting's popularity.
"It's going to be difficult for me to accept a change in authorship," honorary Prado director Jose Manuel Pita Andrade told daily ABC. "We're talking about one of Goya's most extraordinary works."
Jonathan Brown, a New York University art history professor and Prado expert, told AP the brouhaha is simply another example of the unending problem of authorship in old masters' works.
"Every field of Western art has its problem paintings," he said.
