Chael Sonnen tested positive for banned substance during a random testing last month and will not go up against Vitor Belfort at UFC 175 next month.

According to ESPN, the Nevada Athletic Commission conducted a random drug testing last month when Sonnen was in Las Vegas to promote his upcoming fight, and test results confirmed the presence of anastrozole and clomiphene.

Anastrozole is reportedly used to treat early stages of breast cancer, while Clomiphene is used to counter female infertility. Both substances are classified as antiestrogenic.

The UFC light heavyweight campaigner was previously diagnosed with hypogonadism or a case low level of testosterone in his body. Sonnen was allowed to use testosterone-replacement therapy, but the NSAC issued a ban on the use of TRT earlier this year.

Sonnen will likely face suspension for testing positive, but the 37-year-old MMA star insisted that he did not use performance-enhancing drugs, and that he was just forced to look for alternatives after NSAC banned TRT in combat sports.

"These are not performance-enhancing drugs," Sonnen said, referring to anastrozole and clomiphene. "They are not steroids of any kind. It's very tough to be caught in this. They changed the rules. I have to comply with rules. However, there is a transition period. I couldn't have been more open or transparent. Anybody I could talk to about this, I did."

UFC President Dana White, on the other hand, said that he was not shocked after learning that Sonnen tested positive during last month's random drug testing, echoing Sonnen's statement that it was a result of NSAC's rule change on TRT.

"I'm not shocked. This has been lingering," White said. "This stuff has been legal. TRT was legal. Now the (NSAC) said it's illegal. Now it's got to go away, but there's going to be side effects of stopping this thing cold turkey. It just doesn't work that way. When it went away, they didn't do a very good job of figuring out how to get these guys off it. When you get off it, you don't just go cold turkey."

Sonnen also failed a drug test in 2010, testing positive for elevated testosterone-toe-epitestosterone level. He was banned for year, but was later reduced to six months after revealing his medical condition that forced him to use TRT.