U.F.C.’s parent company, Endeavor, has insulated itself from this volatility over the past 18 months through its agreements with ESPN. First, most lower-tier cards were placed on cable television and the company’s ESPN+ streaming service, and later it agreed for ESPN to exclusively sell its pay-per-view fights in the United States.

The contracts guaranteed Endeavor a steady revenue stream it could show potential investors in the run-up to a planned initial public offering this year. But after a delay and lowering its estimated share price, Endeavor canceled its I.P.O. a day before the shares were to begin trading, as the I.P.O. market tanked.

Endeavor and the U.F.C. want to be able to tell a story about growth, and this week in New York, their most fascinating storyteller is more interested in going to war with the U.F.C. than with his actual opponent.

Diaz announced last week that he had tested positive for a banned substance and wouldn’t be fighting on Saturday. But the U.F.C. and the United States Anti-Doping Association quickly clarified that while Diaz had tested positive for an elevated level of a banned substance, it was because of a contaminated supplement and he had not committed an antidoping violation.

If he didn’t actually commit a doping violation, why did Diaz go public?

“It’s making me lose sleep at night,” Diaz said Thursday. “So I’m like, this is war and this isn’t fair. I’m not sleeping. U.F.C. is sleeping. Jorge Masvidal is sleeping.”

After profanely saying he wanted to turn that around, Diaz continued: “ Ain’t nobody is sleeping. Woot woot woot. Fight’s off. Now nobody can sleep, and I was in bed smiling.”

Masvidal, Diaz’s opponent, brings his own circus to the fight. President Trump is expected to attend, one week after he was vociferously booed during a World Series game. Masvidal is one of a number of U.F.C. fighters who vocally support the president.