The father of UFC lightweight champion Abdulmanap, who also serves as a coach, was taken to hospital earlier this month for suspected pneumonia.
He tested negative for Covid-19 but his condition has deteriorated since then and his situation is now critical.
Upon hearing the news, McGregor tweeted, “Praying for the recovery of Abdulmanap Nurmagomedov, a man responsible for more world champions in several combat disciplines than we even know.
“A true martial genius, [I am] very saddened to hear this news this evening. Pray for the Nurmagomedov family right now. ”
UFC president Dana White also reached out to social media for support.
“Abdulmanap Nurmagomedov is a true martial artist who leads a life of pride, honor and respect,” he wrote.
“He instilled these same values in his son, world champion Khabib, from an early age and has always been around for his entire career.
“I know how close Khabib is to his father and I am saddened to learn of his current condition. My thoughts are with Abdulmanap and the Nurmagomedov family while he continues to fight. “
McGregor set aside his feud with Nurmagomedov to publish his statement, days after calling his former enemy “a rat.”
The pair clashed in 2018 with the Russian choking the Dubliner in the fourth round to retain the 155-pound title.
His next fight should take place against Justin Gaethje in September after the American’s superb victory over Tony Ferguson over the weekend.