The former Portugal international tested positive for the banned diuretic furosemide following Fluminense's win over Boavista on 30 March.
The drug is on FIFA's prohibited list as it can be used to hide performance-enhancing substances - but Deco has been quick to issue a statement through his lawyers.
"I talked with my lawyer and I'll wait for the counter-proof," he told Lancenet.
"I have always taken vitamins and never used anything forbidden. I have 18 years of career, 15 in Europe, (without) having had any problem.
"I'll express my opinion only after the [counter-proof] results and I'll go until the end to clarify the facts."