UFC president Dana White said Khabib Nurmagomedov is "officially retired" as he thanked the unbeaten star.
Khabib stunningly announced his retirement after beating Justin Gaethje to defend the lightweight title at UFC 254 in October last year as he improved to 29-0.
White had retained hope of Khabib returning to the UFC, previously talking up the Russian trying to reach a flawless 30-0 record.
But White used Twitter on Thursday to end hopes of a blockbuster comeback for Khabib.
White wrote, with an accompanying picture alongside Khabib: "29-0 it is.
"He is officially retired. It was incredible to watch you work @TeamKhabib.
"Thank you for EVERYTHING and enjoy whatever is next my friend."
Khabib had fuelled speculation he could make a return to the octagon earlier this week.
The undefeated champion posted a photo to Instagram, alongside former UFC co-owner Lorenzo Fertitta, with the words: "It was good to see you Lorenzo.
"@danawhite send me location."