Silva 's opponent , Nick Diaz , was positive for marijuana in a post-fight test .
UFC welterweight contender Hector Lombard had a main - event bout later this year scrapped after testing positive for a performance - enhancing drug following a fight on Jones ' undercard .
Silva 's opponent , Nick Diaz , was positive for marijuana in a post-fight test , and UFC welterweight contender Hector Lombard had a main - event bout later this year scrapped after testing positive for a performance - enhancing drug following a fight on Jones ' undercard .