Thiago Alves (Pictures) tested positive for a banned substance following his stoppage of Tony DeSouza (Pictures) in a UFC-promoted contest, Nevada State Athletic Commission executive director Keith Kizer told Sherdog.com on Thursday.

Alves (10-3-0) could be fined and suspended by the NSAC after trace amounts of spironolactone, a diuretic which could be used to cut weight and mask steroids, was found in the explosive Brazilian welterweight's system. Kizer said post-fight drug tests indicated Alves, 23, was clean of steroids.

Through an American Top Team spokesman, Alves indicated he did not take any diuretics. The fighter conceded, however, that it's possible something could have been in the supplements he ingested leading up to the bout.

Spironolactone, also known as a "water pill," is generally prescribed to treat high blood pressure, swelling caused by congestive heart failure, kidney and liver disease and conditions in which there are abnormally low levels of potassium in the blood, according to WebMD.com.

This marks the first time a mixed martial artist has tested positive for a diuretic in Nevada. Four boxers, including star Ricardo Mayorga, showed traces of Lasix in their systems following NSAC-sanctioned bouts. The hard-hitting Nicaraguan and two other boxers received eight-month suspensions from the NSAC. The fourth, boxer and K-1 fighter Dewey Cooper, will stand in front of the commission Monday.