CHICAGO (WKRC) – A mixed martial arts fighter died at the age of 31 after sustaining a critical injury during the final round of a match.

Isaac Johnson, 31, was fighting against Mario Aleksandrovski at the Matador Fighter Challenge on November 21, according to local outlet NBC 5 Chicago. In the third round of the fight, Johnson suffered a critical injury that required him to be rushed to the hospital at 8:38 p.m.

Johnson was pronounced dead at 12:01 a.m. on November 22.

An autopsy into the cause of Johnson’s death had not been conducted as of Sunday.

The Matador Fighting Challenge advertised itself as “the ultimate MMA and Thai event, where local warriors will battle it out in high-stakes, high-intensity matches” on its website. Johnson’s match against Aleksandrovski was reportedly the 31-year-old’s first Thai boxing match.

“This is a post I hoped to never make,” the event’s promoter, Joe Goyita, said in a Facebook post. “Last night, one of the fighters in our event, Isaac Johnson, collapsed towards the end of his fight. Medical attention was given by medical staff on hand and he was transported to hospital. I was then informed at around 1:30 a.m. this morning that he didn’t make it. I don’t have the words to express how I feel right now, all I can say is my deepest condolences to his family, friends, and teammates.”