UFC lightweight champion Khabib Nurmagomedov retired immediately following his second-round submission victory over Justin Gaethje in a title unification bout on Saturday at UFC 254:
Khabib's father and trainer, Abdulmanap, died on July 3.
"The elder Nurmagomedov had been hospitalized in Moscow since May, when he was diagnosed with the coronavirus," ESPN's Brett Okamoto wrote. "He also underwent heart surgery for a preexisting condition further complicated by COVID-19."
Khabib had not fought since Sept. 2019 prior to his father's death.
Khabib retires with the one of the best resumes in UFC history, if not the best.
He finished 13-0 with the promotion and 29-0 overall during a professional career that started in 2008.
Seven of his 13 UFC wins came via submission or knockout, with the rest being unanimous decision victories. He defended his lightweight belt three times against some of the sport's best fighters in Dustin Poirier, Conor McGregor and Gaithje, all of whom are ranked in the top 11 of UFC's pound-for-pound list.
Per SportsCenter, Khabib's 13-match win streak is tied for the second-longest in UFC history, and he's also tied for the most lightweight title match victories with four.
Khabib entered Saturday second on the list behind Jon Jones, but it will be hard to keep him out of the No. 1 spot following his dominant performance over Gaithje, who was ranked seventh on that same list prior to UFC 254.
Remarkably, Khabib beat Gaithje despite breaking his foot three weeks ago, per White, who mentioned the injury amid other compliments.
UFC welterweight champion Kamaru Usman and Khabib are the only two fighters in the promotion's history to be undefeated with a minimum of 10 fights. Usman is 17-1 lifetime, having lost his second-ever professional fight at CFA 11 in 2013.
As for the future of the lightweight division, Gaethje is the top contender remaining followed by Poirier, Tony Ferguson and McGregor to round out the top four on the UFC lightweight contender list.