Strikeforce light heavyweight Rafael "Feijao" Cavalcante will have to sit out until next May.
On Monday, the California State Athletic Commission upheld his one-year suspension for banned substances.
Feijao tested positive for the steroid Stanozolol after his first-round TKO of Mike Kyle on May 19 in San Jose.
Cavalcante's attorney, Howard Jacobs, argued before the commission during a Monday morning meeting in Los Angeles that his fighter's drug test sample was mishandled, thus the test result should be voided.
But the commission didn't buy the argument and voted unanimously to reject the appeal and uphold his suspension.
The former Strikeforce light heavyweight champion from Sao Paulo is suspended through May 18, 2013 and also responsible for a $2,500 fine.
In other news coming from the meeting, Ed Soares, of nearby Redondo Beach, was approved for a permanent California promoter's license. Soares is best known as the manager for several Brazilian fighters, including Anderson Silva and Lyoto Machida.