Conor McGregor has been told he will not fight at UFC 200 in July.
The Irishman had been due to face Nate Diaz in a rematch in Las Vegas this summer, but had refused to take part in promotional events and announced his retirement earlier this week before retracting it.
McGregor, 27, said on Thursday he wanted his fight with Diaz to go ahead after all, but UFC president Dana White ruled that out in a Las Vegas press conference on Friday night, even as Diaz said he had no interest in any other opponent.
"Anybody who has fought for the UFC over the last 16 years knows that we try to give as much leeway as we can on things," White said.
"But you have to show up to promote the fight. You have to show up to press conferences and shoot the commercials...
"It's part of the job. It's what we do here."
Diaz did attend the press conference along with several other fighters, while McGregor's chair was left conspicuously empty.
Asked who Diaz would now face in the July 9 event, White added: "I don't know. We're going to figure that out. We gave Conor every opportunity in the world to get here.
"We get criticised a lot for bending too much to Conor - and we do. Conor is a guy that has stepped up and fought in big fights on short notice. I respect Conor very much as a fighter and I like him, but you have to show up and do this stuff."
However, Diaz indicated he was only interested in facing McGregor, and said he would go "on vacation" if the fight did not happen.
"I came to fight Conor McGregor and I don't really have too much interest in anyone else," he said. "I don't have any interest in fighting at all. If that's what we were going to do, I thought we were going to do it.
" I didn't ask for that fight, he asked for that fight. If we don't do that fight, I'm going on vacation."
McGregor, who has instead travelled to Iceland to continue his training, appeared to be watching the event as he reacted on social media.
After White said it would be unfair to bend the rules for McGregor when several other fighters had flown in from around the world to attend, McGregor wrote on Twitter: "Everyone flew in. Respect. But not everyone up there made the company 400million in 8 months."
But when the comment was read out to Diaz, the American - who beat McGregor in March - hit back.
"C onor got his ass beat," he said.