Former Chelsea midfielder Deco has failed a doping test in Brazil, with the player's representatives insisting his vitamin supplement was contaminated.
Deco, 35, was tested after Fluminense's clash with Boavista last month and his sample contained traces of furosemide, a banned diuretic which could be used to mask other substances.
Fluminense released a brief statement on their website, refusing to make a decision on possible sanctions and appeals until Deco's 'B' sample is revealed on Friday.
Felleger Ahaz, a spokesman for Deco, told O Globo that the Portuguese player will be prepared to fight any suspension, although protesting his innocence is the main priority as investigations continue.
"The first concern for Deco is defending his image and not with any punishment or suspension," Ahaz said. "He has for a long time taken a vitamin supplement and certainly there has been some contamination."
Deco has been left out of Fluminense's squad for Thursday's Copa Libertadores tie against Emelec.
Information from the Press Association was used in this report.