LAS VEGAS — UFC interim light heavyweight champion Jon Jones has been notified of a potential doping violation, ruling him out of his bout with Daniel Cormier in the main event of UFC 200.

The UFC president, Dana White, announced the dramatic change Wednesday night, three days before the mixed martial arts promotion’s landmark show.

Jones tested positive for a banned substance in an out-of-competition sample taken June 16 by USADA, which administers the UFC’s anti-drug policy.

Jones is considered the top pound-for-pound fighter in MMA, but has failed drug tests around two of his past three scheduled fights. He tested positive for apparent cocaine use before his first fight with Cormier at UFC 182 in January 2015.

Jones served a suspension for much of 2015 after his involvement in a hit-and-run accident.