Shakhtar Donetsk midfielder Fred tested positive in an anti-doping screening during the Copa America in Chile earlier this summer, reports in Brazil have confirmed.
In testing the player's urine, the doping commission found the diuretic hydrochlorothiazide, which is a prohibited substance that can be used as a masking agents for others.
The results of a second test to provide counter-evidence will be released on Tuesday.
The 22-year-old former Internacional man was included in Dunga's 23-man Copa America roster after Wolfsburg midfielder Luiz Gustavo was ruled out with an injury before the start of the tournament.
Despite the late call-up, Fred emerged as a starter in Brazil's first two games in Chile before losing his place in the Selecao's 1-0 loss to Venezuela in the final match.
Brazil crashed out at the quarterfinal stage for the second straight year in Chile, losing to Paraguay on penalties.