UFC light heavyweight Chael Sonnen's fight with Vitor Velfort at UFC 175 was cancelled Tuesday after a failed drug test.
Sonnen was subjected to a random test last month by the Nevada State Athletic Commission that found anastrozole and clomiphene, two banned substances that are normally used to treat breast cancer patients and female infertility, respectively.
UFC officials confirmed the results. "UFC officials acknowledge irregularities in a recent random test. Chael is planning on addressing the matter."
The 37-year-old fighter is likely to face a suspension from UFC.
It's the second time Sonnen has failed a drug test. In August 2010, he tested positive for elevated testosterone before a fight against Anderson Silva and was suspended for one year by the California State Athletic Commission.
Sonnen (28-14-1) also works as an UFC analyst for Fox Sports.