The will-he or won't-he saga of whether Paulo Costa would be able to fight Khamzat Chimaev on Oct. 21 in Abu Dhabi, United Arab Emirates ended Wednesday afternoon when Costa was declared medically unfit and former welterweight champion Kamaru Usman stepped up to fill the spot.

UFC CEO Dana White announced the change on social media.

The bout between Usman and Chimaev will be held at middleweight, and the winner will get the next crack at the middleweight title, White told Yahoo Sports. The Chimaev-Costa fight had been set to be a middleweight bout and Usman was looking to move up after losing back-to-back welterweight title fights to Leon Edwards.

Costa had surgery on his right elbow because of bursitis and was deemed unfit to go with the fight so close. In stepped Usman, who hasn't fought since March 18 when he lost to Edwards in London.

The fight will pit Chimaev, No. 4 in the UFC's welterweight rankings, against Usman, whom the UFC ranks No. 7 pound-for-pound. With the main event featuring No. 2 Alex Volkanovski against No. 3 Islam Makhachev for the welterweight title, the card features three of the top seven pound-for-pound fighters in the world. Chimaev is ranked No. 5 pound-for-pound by Yahoo Sports, Volkanovski is No. 2 and Usman is No. 7.

Usman is a wrestler like Chimaev, while Costa is known as a powerful striker. White thinks the change could make it a better fight.

"Who knows how they'll approach it, but you have to think that with the Costa fight, Khamzat probably had to be thinking about going out and taking him down," White told Yahoo Sports. "But with Usman and his wrestling, it could actually turn into more of a stand-up war."

Chimaev is a takedown machine, but Usman's takedown defense is 97.3, first in UFC history.

White was in a gleeful mood after putting together Makhachev-Volkanovski after Charles Oliveira withdrew because of a bad cut and then Chimaev-Usman after Costa's issues.

He was more ecstatic than normal when discussing the fighters in the main and co-main.

"This is what fighting should be," White said. "I don't know if you saw what [former lightweight champion] Khabib [Nurmagomedov] said. He said, 'Brother, we are UFC champions. You fight King Kong if he makes weight.' That's what makes fighting so fun. They're all taking these fights just over a week out and they're all accepting risk. They believe in themselves. And to my way of thinking, this is what makes this sport so great, when you have world champions or guys who are top five in the world and that's their mindset.

"When that's the case, there's no better sport in the world. That's what makes the UFC so great, the mentality of these fighters."