Spanish customs seize Picasso sketch at Ibiza airport. AFP
Agents found the 1966 sketch, dubbed "Trois personnages", on July 5 in the suitcase of a man who arrived in the holiday island on a flight from Zurich, the office said in a statement.
The passenger said the artwork was a simple copy and presented the agents with a handwritten receipt of 1,500 Swiss francs (1,515 euros) which he said he had paid for the sketch.
But customs agents found another receipt in the bottom of his suitcase from a Zurich art gallery for 450,000 Swiss francs (454,000 euros) with a reference to a work by Pablo Picasso called "Trois personnages".
According to a preliminary analysis carried out by art experts, the sketch is indeed a work by the Spanish painter and "the price charged by the gallery is in line with the market price," the statement said.
This first assessment will have to be confirmed by a "more exhaustive" analysis using "advanced techniques", it added.
The passenger faces possible charges of smuggling for failing to declare an object of value when he entered Spain.
The customs office said they had singled him out for questioning after receiving a tip from their Swiss counterparts that he was transporting a piece of art in "suspicious" conditions.
Considered to be one of most famous artists of the 20th century, Picasso spent the bulk of his long life in France, dying there in 1973.