Francisco Rivera popped for potential doping violation

Francisco Rivera is the latest in a growing list of UFC fighters to have a potential doping violation.

The UFC confirmed Wednesday that Rivera was flagged by the USADA for a banned substance in an out-of-competition test taken July 23, just one week before he fought Erik Perez at UFC 201, losing by unanimous decision.

The UFC anti-doping policy, administered by the USADA, allows Rivera the right to a legal review before any ruling is decided.

Rivera was reportedly informed he tested positive for clenbuterol. The bantamweight claimed he was in Mexico before the test, and cited tainted meat as the potential cause of the violation, MMA Fighting's Marc Raimondi reported Thursday

In 2011, the World Anti-Doping Agency issued a warning for clenbuterol-tainted meat in Mexico and China.

Fellow UFC fighter Ning Guangyou, who is from the latter nation, recently tested positive for clenbuterol, stemming from tainted meat. He was cleared of any wrongdoing and is scheduled to fight at UFC on FOX 21 next week.