Adesanya and Costa are set to collide in the main-event of UFC 253 on September 26.
And ahead of their championship bout, the Brazilian challenger has issued his most controversial message yet to the Nigerian-born Kiwi title holder.
Speaking to Submission Radio, Costa questioned Adesanya's approach in his last fight and says he'll kill him in the Octagon.
"I have just one question," he began. "Adesanya, why you freezing when you face Romero? You're not a real champion, man. You don't deserve. I will kill you."
The 29-year-old added: "I like to think of myself like a real tough guy, maybe the toughest guy on the planet.
"Because I train very hard, with two, three guys at the same session training, with very hard hits, very hard punches, very hard kicks for real.
"100 percent, I mean. Not just fake, just shadowboxing. No. So, this makes me very prepared to fight in real fights with real opponents like Romero.
"I am not afraid to get hit, because I did this already in my fight camp for two or three months. So, I'm properly prepared to make it a real fight."
Adesanya last fought in March when he outpointed Yoel Romero in an underwhelming fight at UFC 248.
Costa, meanwhile, hasn't fought since his 'Fight of the Night' victory over Romero at UFC 241 last year.
Featured Image Credit: PA/Twitter
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