MADRID (AFP) - Lionel Messi's spotless image as the world's greatest footballer and a humble man has taken a stunning blow with accusations that he cheated on his taxes, the Spanish media said on Thursday.

Newspapers reacted with shock to news that the Barcelona star and Argentina international has been accused of defrauding the Spanish tax authorities of more than 4 million euros (S$6.6 million).

"A symbol under suspicion," blared the front page of the country's biggest sports daily, Marca, saying in an editorial that the four-time World Player of the Year had cast doubt on his image as an exemplary sportsman.

"He has not been condemned, just accused, but the tax authority's account of a supposed fraud is hair-raising," the paper said, adding that the revelations were a surprise.

Madrid-based daily El Mundo said the claim "smears his image" and if proven would be "extraordinarily serious" and should be doubly condemned because of the 25-year-old's high income.

The Argentine was ranked 10th amongst Forbes' list of sports stars' incomes this month with an annual US$21 million (S$26 million) from endorsements alone.