Former top middleweight contender Chael Sonnen failed a random drug test and will not face Vitor Belfort on July 5 at UFC 175 in Las Vegas.
Sonnen was removed from the card after results from a test conducted in May by the Nevada State Athletic Commission revealed he had illegal substances -- anastrozole and clomiphene -- in his system.
ESPN.com first reported the news on Tuesday.
"UFC officials acknowledge irregularities in a recent random test," the promotion stated. "Chael is planning on addressing the matter this afternoon."
Anastrozole is used to treat breast cancer in women going through menopause, according to MedicineNet.com.
Clomiphene is used to stimulate ovulation.
Sonnen, 37, is expected to address the matter Tuesday night on Fox, where he is an MMA analyst.
Sonnen (28-14-1) was originally slated to face Wanderlei Silva at UFC 175. But Silva refused to submit to random drug tested and was removed from the event last month.
Belfort's status for the event remains uncertain. He received testosterone replacement therapy approval during his three previous bouts, none of which were held in Nevada. Belfort claims he has discontinued the use of TRT. He is scheduled to attend a NSAC licensing meeting on June 17.
Sonnen was seeking to rebound from a first-round TKO loss to former light heavyweight champ Rashad Evans in November at UFC 167. He has struggled of late, having lost three of his four most recent fights.
Belfort, also 37, is currently riding a three-fight win streak. He has won five of his past six fights, and has a professional mark of 24-10.
Middleweight champ Chris Weidman puts his belt on the line against former light heavyweight titleholder Lyoto Machida in the UFC 175 main event. The card takes place at Mandalay Bay Events Center.
Women's bantamweight champion Ronda Rousey defends against highly touted Alexis Davis in the co-feature.
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