Cris "Cyborg" Justino has been notified of a potential U.S.Anti-Doping Agency violation stemming from an out-of-competition Dec. 5 drug test.
The drug in question has not been identified in accordance with USADA policy.
UFC released a statement on Thursday acknowledging the potential violation.
"USADA, the independent administrator of the UFC Anti-Doping Policy, will handle the results management and appropriate adjudication of this case. It is important to note that, under the UFC Anti-Doping Policy, there is a full fair legal review process that is afforded to all athletes before any sanctions are imposed.
"Consistent with all previous potential anti-doping violations, additional information or UFC statements will be provided at the appropriate time as the process moves forward."
Justino, 31, has been suspended for a doping violation before, drawing a one-year suspension in 2011 after testing positive for the steroid stanozolol.
Justino has a 17–1 UFC record and has won all seven of her fights since returning from her suspension.
She has not yet commented on the news of the potential violation.