Fred tested positive on a doping test during the Copa America, Brazil’s football association (CBF) has confirmed.
The Shakhtar Donetsk star, 22, had banned substance hydrochlorothiazide in his bloodstream, which can act as a masking agent to hide illegal drugs from testers.
The CBF said in a statement on Friday that it had provided a list of medications and their usages to organisers two months before the start of the Copa America.
Hydrochlorothiazide was not part of the list, nor was it available to the CBF, the confederation said, but it stressed Fred had its support.
Fred started two games for Brazil as they reached the quarter-finals in Chile before being knocked out by Paraguay.
Uefa is currently investigating Shakhtar Donetsk’s decision to field Fred in Tuesday’s Champions League third-round qualification first leg following a complaint from Fenerbahce, with whom they drew 0-0.