MMA world lightweight champion Khabib Nurmagomedov announced his shock retirement from the sport on Saturday after revealing he "promised his mother" that his clash with Justin Gaethje would be his last fight.

The Russian, who won by a second-round technical knockout, was fighting for the first time since the death of his father and coach Abdulmanap in July.

"I'm the UFC undisputed, undefeated champion with a 13-0 record (in UFC), and 29-0 in all of my pro MMA career," he said after his win in Abu Dhabi.

"Today I want to say this is my last fight. No way am I coming here without my father. When UFC comes to me about Justin I spoke with my mother for three days. She didn't want me to fight without father and I said this is my last fight – and I have given her my word."

"Thank you so much Justin. I know you are great, I know how you take care of your people. Be close with your parents, because you never know what is going to happen tomorrow. Thank you coach, thank you guys. Today is my last fight in the UFC.

"It was my father's dream. Justin and Conor (McGregor) will fight in January, I have choked both out, I am not interested in this," he added.

Abdulmanap Nurmagomedov, 57, passed away after suffering complications from COVID-19 in the summer.

Long time rival McGregor of Ireland, who lost to Nurmagomedov in 2018, was among the first to congratulate the 32-year-old Russian on his career.

"I will carry on. Respect and condolences on your father again also. To you and family. Yours sincerely, The McGregors," he tweeted.

UFC president Dana White joined the tributes and revealed at a news conference as Fight Island ended that Nurmagomedov had broken his foot in the build-up to Saturday's event.

"What this guy's been through, we're all lucky we got to see him fight tonight," said White.

"Apparently he was in the hospital. He broke his foot three weeks ago. So he has two broken toes and a bone in his foot that's broken – that's what his corner was telling me. Never told anybody.

"He is one of the toughest human beings on the planet and he's the number-one pound-for-pound fighter in the world and, seriously, you have to start putting him up there with GOAT (greatest of all time) status with whoever else you think is the GOAT."

(With input from agencies)