The situation regarding George Sullivan and his potential USADA issue is uncharted territory for the UFC.

The UFC welterweight released a statement Thursday night on Facebook, writing he was "shocked" that the promotion pulled him from his UFC on FOX 20 fight with Hector Urbina earlier in the day. The card is scheduled for Saturday night in Chicago.

In the statement, Sullivan said he was removed from the bout because of a "natural supplement" that appeared on a list of things he was taking that was submitted to USADA and the UFC. USADA is the UFC's anti-doping partner.

"I did not fail a test," Sullivan wrote. "I was pulled from the card due to a natural supplement being on my list of supplements that I voluntarily disclosed to USADA. This supplement has been on my list that I have disclosed to both the UFC and USADA prior to my previous fights."

Sullivan, 35, has competed in the UFC twice since USADA became the promotion's anti-doping partner in July 2015. Sullivan said he has been tested by USADA and other organizations before and has never tested positive for any banned substance. The USADA website says Sullivan has been tested twice this year by the agency.

"I plan to do whatever it takes to clear my name," Sullivan said. "I am confident that my name will be cleared."

In a statement Thursday night, USADA said Sullivan made the agency aware of a "high risk" dietary supplement he was using during an out-of-competition sample collection July 13. USADA said Sullivan never declared he was using that supplement previously.

Sullivan is not currently facing a potential anti-doping violation or sanctions, but USADA said it will investigate the matter due to the "strong possibility that the product he declared contains a prohibited substance."

The full USADA statement is as follows:

"Given that the athlete has publicly addressed this matter, USADA can confirm that it has initiated an investigation following Mr. Sullivan's declaration of a high risk "dietary supplement" during an out-of-competition sample collection on July 13, 2016. At no time prior to last week had Mr. Sullivan made this declaration during a USADA sample collection. As of now, USADA has not concluded that a policy violation was committed and Mr. Sullivan has not been notified of a potential anti-doping policy violation. Nonetheless, given Mr. Sullivan's declaration, and the strong possibility that the product he declared contains a prohibited substance, USADA will continue to thoroughly investigate the matter."

The UFC announced Thursday afternoon that Sullivan was off the card because he might be out of compliance with the promotion's anti-doping policy. The UFC said it was taking Sullivan out of the fight "out of an abundance of caution" and that USADA would investigate the matter.

The UFC's full statement is below:

UFC competitor George Sullivan voluntarily disclosed information to the U.S. Anti-Doping Agency (USADA) that could pose a potential compliance issue with the UFC Anti-Doping Policy. Out of an abundance of caution, Sullivan has been removed from his scheduled bout on Saturday night against Hector Urbina while USADA conducts an investigation into the matter. Urbina will still weigh in as a potential backup opponent should there be a need for him to compete in another bout on Saturday. Otherwise, he will be re-booked for another card in the near future.

Sullivan (17-5, 1 NC) last fought in January at UFC on FOX 18, a first-round knockout loss to Alexander Yakovlev. The New Jersey native and former Cage Fury Fighting Championships welterweight champion is 3-2 in the UFC and has been a pro fighter since 2006.