LAS VEGAS — Absolute nightmare for Conor McGregor truly came out of nowhere.

The “Notorious” Conor McGregor threw a crazy head kick at opponent Max Holloway that didn’t fully land in his quick UFC 329 loss on Saturday night at T-Mobile Arena.

McGregor landed wrong on his right knee, fell to the ground, and appears to have torn at least one ligament in his knee.

A source told The Post McGregor did not enter the fight injured and was fully healthy before throwing that head kick.

McGregor had been practicing that wild head kick as recently as this week, throwing it over and over as he prepared to pounce on Holloway.

“We’re assuming it’s a blown ACL,” Dana White said to reporters after McGregor’s loss.

McGregor took to X after the bout, saying he was healthy heading into the fight.

“My head gasket is gone. Destroyed. I had no injury / injuries going into the fight. I was throwing kicks, planted and jumping, all throughout camp as well as backstage before the fight. This came out of nowhere. I am beyond dark here. I can only describe it as hell.”

The speculation that this injury was preexisting had run rampant immediately following the injury, and fans expressed their displeasure with boos following the event, perhaps feeling they were duped with a comeback story.

“I don’t think there was a pre-existing injury,” White told reporters. “The ceremonial weigh-in video had over 80 million views; someone would have noticed.”

A reporter questioned whether the injury may have happened after the ceremonial weigh-ins, but I’m told that is not the case.

His knee just bent the wrong way, and he now faces a disastrous outcome where he likely will need surgery if the worst-case scenario is realized with a torn ACL.

McGregor is expected to undergo an MRI exam within the next few hours, but the 37-year-old McGregor may face another year-long layoff after hoping to fight within the next nine months.

He is on the last fight of his contract before he may enter free agency.