Cypress, Sky and Country went missing from Vienna's Art History Museum around 40 years ago, Spain's El Mundo newspaper reported.
Art experts have told Spain's Tax Office the work painted in 1889 and measuring 35 by 32 centimeters 13.7 by 12.5 inches is probably genuine, citing the evidence of three seals as proof. One of those is from Holland's Rijksmuseum museum, and is dated to 1944, or during Nazi occupation of the country.
The authenticity of the painting is now to be verified by the country's ministry of culture.
But an Austrian art expert has thrown on the origins of the painting.
Dr. Friedrich Polleroß, head of the archives of the Art History Institute of Vienna University told The Local Austria the university had no records of seeing such a painting in the Art History Museum.
The museum also denied knowledge of ever having had such a painting in its collection.
An additional red flag is that Vienna University already received an inquiry about this painting from the Criminal Police of Berlin in November 2013.
The painting in question was discovered during an investigation into tax fraud worth €319 million ($439 million), Spanish tax authorities said. The painting turned up during a search through 542 safety deposit boxes in 270 bank branches.
The search also turned up 15 bullfighting costumes, jewellery and €2 million in cash, which has now gone into tax office coffers.
The investigation is part of the Spanish tax office's ongoing attempts to boost tax collection during the country's economic crisis. Recently, it was reported the agency was selling off seized goods including bras, sunglasses and children's pencil cases.