Several hours after featherweight champion Conor McGregor sent out a tweet announcing his retirement, UFC president Dana White announced on "SportsCenter" Tuesday that the Irish superstar has been yanked from the main event of UFC 200 opposite Nate Diaz.

The announcement marked a stunning turn of events in a strange day that began with what many regarded as a joke when McGregor tweeted he had retired. McGregor on Monday announced via social media that he had arrived in Reykjavik, Iceland, to train.

On Tuesday, at approximately 2:30 p.m. ET, he wrote on Twitter, "I have decided to retire young. Thanks for the cheese. Catch ya's later."

There was silence for the next 5 1/2 hours, as White and McGregor manager Audie Attar failed to return numerous messages seeking comment. But at around 8 p.m. ET, White appeared on "SportsCenter" and said McGregor had been pulled from the card for refusing to fly to Las Vegas to participate in a news conference as well as to take promotional photos.

"Well, what's happened is, we've pulled Conor McGregor from UFC 200," White said on "SportsCenter." "And we're working on other fights right now. Conor did not want to come to Las Vegas [this week] to film the commercial or be a part of any of the marketing that we have. He's in Iceland training and [not participating in the marketing] is not possible. This has only happened one other time in UFC history.

"Nick Diaz didn't show up for his press conference for his fight with Georges St-Pierre and I pulled Nick Diaz from the fight. We've had other instances like this where guys didn't want to do the press conference, [but] you have to. You have to do the press conference, so Conor put out that tweet. Is Conor McGregor retiring? Only he could answer that question."

Yahoo Sports reached out again to White following the "SportsCenter" announcement, which he did via telephone. He was in San Francisco and, according to UFC spokesman Dave Sholler, unavailable to comment until at least 10 p.m. ET.

UFC Chairman Lorenzo Fertitta and COO Lawrence Epstein were traveling as well and unavaible for comment. Attar also failed to return messages.

White told "SportsCenter" that Diaz is flying to Las Vegas on Tuesday evening and the UFC is attempting to put together another fight for him at UFC 200. He said the promotion is looking to add another high-profile bout to the UFC 200 show.

Whether this marks a serious rift in the relationship between UFC officials and McGregor remains to be seen. But White attempted to downplay that in his brief appearance on ESPN.

"Obviously, we still have a good relationship with Conor," White said. "I respect Conor as a fighter and I like him as a person. [But] you can't decide not to show up to these things. You have to do it. We were in constant communication back and forth between his manager and myself. I said, 'Listen, I'm flying out of here at 2 o'clock. You have until 2 o'clock. We're booking the flight for you and you have to say you're accepting the fight and you'll show up [in Las Vegas this week for the promotional activities.]' "