Argentine authorities have opened an investigation into the financial affairs of tennis star Juan Martin del Potro, who is suspected of tax evasion, officials said Monday.

Local press reported that the case against del Potro, ranked 13 in the world, involved prize money from 2010, the year after he won the US Open.

“It is true that an investigation over tax evasion has been opened against del Potro,” said a judicial source told AFP on condition of anonymity.

In a letter published in Perfil newspaper, the 25-year-old denied the allegations and pledged to cooperate with investigators.

Del Potro, the highest-ranking Argentine player, has been out of action since February because of a wrist injury.