Romero was flagged by the U.S. Anti-Doping Agency for a potential violation of the UFC's anti-doping policy for an out-of-competition test. The news of the violation was made public about a month after Romero defeated Ronaldo Souza at UFC 194.
The 38-year old American Top Team fighter is still awaiting the results of his B-sample test, MMAFighting.com's Ariel Helwani reported on Wednesday's edition of UFC Tonight.
According to Romero's agent, Malki Kawa, the fighter disputes the results of the test, saying he passed all tests administered before the one which came up positive and all tests conducted since. They will file a formal appeal as soon as the B-sample returns from the lab.
A lot rides on the results of the B-sample and Romero's appeal. Romero's victory over Souza appeared to put him in position for the next shot at Luke Rockhold's UFC middleweight title. But with a two-year ban for first offenders under new performance-enhancing drug rules, a suspension would mean Romero would be 40 by the time he returned to competition.