According to Spanish newspaper, El Mundo, Costa pleaded guilty to a tax offence amounting to €1.1million.
The former Chelsea star was accused of defrauding the treasury of more than £900,000 by not declaring payments of more than €5.15m (£4.63m) after his move to Chelsea in 2014.
The Spanish treasury denounced the 31-year-old for defrauding the authorities regarding €1m (£890,000) in image rights.
The tax agency added another fiscal crime to Costa before withdrawing and halving the fine.
Costa has now agreed to pay €36,000 fine to avoid any jail time.
