UFC welterweight contender Nick Diaz failed his post-fight urinalysis Saturday following his loss to Carlos Condit in their bout for the interim welterweight championship at UFC 143 at the Mandalay Bay Events Center, Keith Kizer, executive director of the Nevada Athletic Commission, announced Thursday.

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Diaz, 28, who tested positive for marijuana, is a second-time offender in Nevada and, thus, faces a one-year suspension. He also tested positive for marijuana following a Feb. 24, 2007, victory over Takanori Gomi at a PRIDE Fighting Championship event held at the Thomas & Mack Center in Las Vegas.

Six weeks after the first positive test the commission fined Diaz $3,000 (20 percent of his $15,000 purse), suspended him for six months and changed his win over Gomi to a no-decision. The commission’s report in 2007 noted Diaz’s concentration of THC, the active ingredient in marijuana, was 175, three-and-a-half times the concentration level of 50 required under Nevada regulations to produce a positive test result.

“All results received thus far have been negative, except Mr. Diaz tested positive for marijuana metabolites,” Kizer said in a release Thursday. “A complaint for disciplinary action against Mr. Diaz has been filed.”

Diaz isn’t the first fighter to test positive for marijuana recently. Matt Vanda appeared before the Nevada commission Jan. 31 after a second positive test for marijuana. He had initially been suspended for 90 days by the New Jersey State Athletic Control Board after marijuana was discovered in his system following a Nov. 12, 2010, bout against Ossie Duran.

Marijuana was again found in Vanda’s system following a Dec. 16, 2011, loss to Marco Antonio Rubio in Las Vegas and on Jan. 31 the Nevada commission fined Vanda 40 percent of his $11,000 purse and suspended him for a year.

If Diaz is fined 40 percent of his purse, it would cost him $80,000 of the $200,000 he earned in the unanimous decision loss to Condit last Saturday for the UFC interim welterweight title.

Diaz was on the verge of getting a rematch with Condit for the interim championship when the test results returned and scuttled the bout. UFC president Dana White, in Brazil to tape “The Ultimate Fighter: Brazil,” sent out a message on Twitter late Tuesday in which he said Condit had agreed to a rematch.

But all sides denied Wednesday that a rematch had been agreed upon before news of the positive test result was released Thursday.

UFC CEO Lorenzo Fertitta said he was “disappointed” to hear of Diaz’s positive test. He said the UFC would honor any punishment Diaz was given and would not seek to have him fight in areas which are not regulated.

When the UFC holds events out of the U.S., if there is not a local body that regulates the sport, the UFC self-regulates. Marc Ratner, the UFC vice president for regulatory affairs and Kizer’s predecessor as executive director of the Nevada commission, runs those events under Nevada rules.

“We would stand behind whatever decision Nevada makes and if Nick is given a punishment, we would accept it,” he said. “Marijuana is an illegal substance and if you choose to take that, you have to pay the price for it.”