Israel Adesanya's remarkable career in combat sports has come to a major crossroads, following his fourth defeat in five appearances on Saturday.

Adesanya (24-5) suffered a TKO loss to Nassourdine Imavov (16-4) at the 30-second mark of the second round. Imavov rocked Adesanya with a right hand to the chin and followed with a strong left to his chin, after Adesanya crashed backward to the fence. Referee Marc Goddard gave him a chance to respond, but once Adesanya rolled onto his stomach and covered up, the fight was over.

The nontitle bout, which was Adesanya's first non-championship appearance since 2019, headlined UFC Fight Night in Riyadh, Saudi Arabia. A win would have kept him in title contention -- while a loss throws his entire future in the sport into question. For Imavov, it's the biggest win of the 28-year-old Frenchman's career, and now has him eyeing his first shot at UFC gold.

"I said it all week long, that I was in perfect shape and I proved it tonight," Imavov said through an interpreter. "I proved I was a better striker and now, the real bonus for me is going to be fighting for the belt. There is no doubt I am ready for the belt. Four victories in one year -- the record speaks for itself."

Adesanya, 35, took nearly a year off to regroup in 2024, after losing his belt in a shocking upset to Sean Strickland in September 2023. He returned to an immediate title shot against Dricus Du Plessis in August, and lost via submission in the fourth round.

He was favored to defeat Imavov, 29, on Saturday, but he failed to produce much of his historical magic. He targeted Imavov's body with kicks and outlanded him in total strikes 32-to-18 according to UFC Stats -- but his volume style has lacked its effectiveness in this 1-4 skid. He has now been knocked out twice in less than three years, after going his entire MMA career without being knocked out previously.

Current champion Du Plessis (22-2) is scheduled to defend his title in a rematch against Strickland (29-6) in the main event of UFC 312 next weekend in Sydney. The undefeated Khamzat Chimaev looms as a potential title challenger beyond next weekend's contest, but Imavov is now firmly in the conversation as well.

Adesanya, who was born in Nigeria and now lives and trains out of New Zealand, appeared to briefly question the referee's decision to stop the fight immediately after returning to his feet, but left the Octagon without incident shortly after.

"I have to chill and then think about things," Adesanya said on the UFC post show. "I will relax first for a little bit, just help the teammates who have fights coming up and see what I want to do. I was going to do that anyway, but now I'm forced to. Shoutout to Nassourdine for that."

UFC CEO Dana White did not seem concerned about Adesanya's prospects moving forward, despite his recent skid. White praised Adesanya's performance in the opening round, which all three judges did score in his favor.

"I thought Izzy looked incredible until he got caught," White said. "He was picking him apart, staying on the outside, takedown defense was incredible, chopping that calf kick. That whole round, he couldn't have had a better first round, but then he got caught."