UFC Lightweight champion Khabib Nurmagomedov's father, Abdulmanap Nurmagomedov, died Friday at the age of 57. 

According to RT.com (h/t CNN's Ben Morse), Abdulmanap died in a Moscow hospital from complications related to COVID-19.

Khabib's manager, Ali Abdelaziz, told ESPN's Brett Okamoto in May that Abdulmanap was in a medically induced coma after being diagnosed with the coronavirus:

"I can confirm Khabib's father is in a medically induced coma. Khabib has been in contact with [Russian president] Vladimir Putin over the last several days, and he has promised Khabib's father will receive the best medical treatment available. Khabib's No. 1 message to people around the world right now is to stay at home, to prevent the spread of coronavirus."

Abdulmanap had previously undergone heart surgery as well, and he was airlifted from Dagestan to Moscow in May.

One of Khabib's greatest rivals, Conor McGregor, expressed his condolences Friday on Twitter:

Conor McGregor @TheNotoriousMMA

The loss of a father, a coach, and a dedicated supporter of the sport. Condolences and rest in peace Abdulmanap Nurmagomedov.

In addition to being Khabib's father, Abdulmanap was the undefeated fighter's trainer for many years. Abdulmanap was well-versed in several disciplines, including wrestling, judo and sambo.

Abdulmanap was also the coach for the combat sambo national team in his native Dagestan.

Under Abdulmanap's guidance, Khabib owns a 28-0 professional MMA record with 10 wins by way of submission and eight by knockout. He defeated McGregor by submission at UFC 229 in 2018 and beat Dustin Poirier by submission at UFC 242 in his most recent fight last year.

Khabib had been scheduled to face Tony Ferguson at UFC 249, but travel restrictions in place because of COVID-19 prevented him from doing so.