Chael Sonnen has been fired from his job as co-host of FOX Sports' "UFC Tonight" show after failing a second drug test in the past six weeks, the UFC and the network announced Monday night.

Sonnen had tested positive for banned substances in May and was removed from the UFC 175 card scheduled for Saturday in Las Vegas. He then failed another drug test in mid-June, leading to his dismissal from the show as the sport attempts to combat the use of performance-enhancing drugs.

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"The UFC and FOX Sports organizations announced today the termination of their respective broadcasting services agreements with analyst Chael Sonnen," said a joint statement released Monday by the UFC and Fox Sports. "This decision comes in light of Sonnen failing a second test conducted by the Nevada Athletic Commission for banned substances in June. Sonnen was previously under temporary suspension by the Nevada Athletic Commission for failing an initial test conducted in May."

Sonnen, who in the past has been granted exemptions to use testosterone replacement therapy (TRT) before the Nevada Athletic Commission banned it last February, was tested in May. On June 10, it was revealed Sonnen tested positive for anastrozole, a non-steroid used to treat breast cancer, and clomiphene, which can be used to treat female infertility. On June 11, he retired from MMA from his on-air seat as co-host of "UFC Tonight."

Sonnen was then randomly tested in June, which produced a positive result for human growth hormone and recombinant human erythropoietin (EPO).

Sonnen was scheduled to fight Wanderlei Silva at UFC 175, but Silva refused to take a drug test and was removed from the card. Vitor Belfort, who also was granted theraputic use exemptions for TRT in the past, , replaced Silva, but the Sonnen-Belfort fight was scrapped when Sonnen first tested positive.

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"We will support the commission," UFC director of communications Dave Sholler said Saturday night at a UFC event in San Antonio, "and continue to ensure that all UFC competitors compete on an even playing field free of performance enhancing drugs and banned substances."