In an unprecedented move, the UFC has decided to switch their end-of-year UFC 232 event from Las Vegas to California in order to allow main event star Jon Jones to compete in a world title fight.

Jones was scheduled to face Sweden's Alexander Gustafsson in the main event at the T-Mobile Arena in Las Vegas, but on the night of December 23 news emerged of an anti-doping discrepancy involving the controversial former world champion.

The Nevada State Athletic Commission (NSAC) confirmed they would not license Jones to compete at the December 29 event after the American registered an "abnormality" in a pre-fight drug screening.

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An anti-doping test conducted on Jones earlier in December discovered a trace amount of turinabol, the same substance that saw Jones suspended for 15 months in 2017.

Jones was subsequently cleared from that suspension after a lengthy appeals process and the provision of "substantial assistance" and was immediately booked to fight Gustafsson on the UFC's year-end event.

But now, as a result of the flagged test, the Nevada Commission will not sanction Jones' fight until he has gone through an appropriate process, starting with a hearing in January.

With the UFC set to lose their huge main event from UFC 232, they instead announced on Sunday night that the event would be switched from Las Vegas to Los Angeles, California, with UFC 232 now set to be held at The Forum in Inglewood.

The California State Athletic Commission has cleared Jones to fight, based on their own assessment of his situation, with CSAC executive officer Andy Foster laying out the reasoning for the Commission's decision in a statement to US outlet MMA Fighting.

"We’ve got a statement from three different scientists, from the lab director saying there’s no evidence of any new ingestion," Foster explained.

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"This isn’t a new thing. This is what he’s been punished for already. He’s already served his time on this."

Foster also revealed that Jones had already flown to California for a subsequent drug test, which he passed.

"He’s a clean athlete," Foster said.

Meanwhile, the UFC's independent anti-doping contractors USADA released a statement of their own, saying the trace amount discovered would offer no performance-enhancing benefits to Jones, and that the amount found was most likely to have been from his previous ingestion of the substance.

USADA Statement on Jon Jones Sample and UFC Anti-Doping Policy pic.twitter.com/TJfbJB5X9W — USADA (@usantidoping) December 23, 2018

"There’s been no violation of the anti-doping program," UFC vice president of athlete health and performance Jeff Novitzky told members of the media on Sunday.

"He’s been cleared to fight in terms of the USADA program. USADA fully analyzed it internally. They reached out to outside experts from around the world. They reached out to another sports league that has seen the same issue.

"All of them, independent of us, determined that this was not a re-ingestion of the substance and this very, very small amount that was occurring and still showing up, according to these experts from around the world, did not provide any performance-enhancing benefit.

"Not much is known about this longterm metabolite. The parent compound is not approved for human use anywhere in the world. But what both USADA and other entities are seeing is that a recurrence, or potential 'pulsing,' where you have multiple negative tests and then a positive one for a very low amount – they’re seeing that quite commonly over time. And no one knows how long this could last [in Jones' system] – it could potentially last forever."

The event at The Forum marks only the second occasion the UFC has held an event at the famous California venue.

The promotion's only other visit came on June 4, 2016, when Britain's Michael Bisping knocked out Luke Rockhold to win the UFC middleweight title at UFC 199.