UFC lightweight champion Khabib Nurmagomedov's father and coach, Abdulmanap, has died aged 57 following complications caused by coronavirus.
Abdulmanap, an MMA coach, was taken to hospital in Moscow in May, after coronavirus symptoms exacerbated an existing heart condition.
The news of his death was confirmed by Khabib's manager, on Twitter on Friday.
Khabib is unbeaten in 28 bouts,
McGregor offered his condolences, tweeting: "The loss of a father, a coach, and a dedicated supporter of the sport."
McGregor said he was "praying for the recovery" of Abdulmanap after learning of his critical condition.
Having been treated initially in his native Dagestan, army veteran Abdulmanap was flown to a military hospital in Moscow when his condition worsened.
The former wrestler also coached several other world champions across different combat disciplines, including current UFC fighter Islam Makhachev.
Abdulmanap was in his son's corner last September when Khabib successfully defended his lightweight title against Dustin Poirier.