Watch Now: Jorge Masvidal's Long Journey To A Title Shot (2:16)

Mike Brown, a key member of Jorge Masvidal's corner, will be unable to coach his fighter in the biggest bout of his career on Saturday after testing positive for COVID-19. Masvidal stepped in on late notice to face welterweight champion Kamaru Usman in the main event of UFC 251, with the fighter and his team all taking multiple tests for the coronavirus prior to traveling to Yas Island in Abu Dhabi for the event.

Brown, a former WEC featherweight champion, is a member of American Top Team and has established himself as a top coaching mind since retiring from active competition, including playing an integral role in Masvidal's journey to becoming one of the UFC's top stars.

"Just heartbroken I'm not going to see Jorge win the world championship in person," Brown said in a statement given to ESPN. "Nobody deserves it more than this guy. Nobody has paid more dues. Jorge is also one of the most thoughtful athletes I've ever met. He makes everyone feel they are with him and a huge part of this journey.

"The truth is this guy has been honing his skills for more than 20 years and developed one of the highest fight IQs the sport has ever seen. As far as being COVID positive, I feel good. The only pain I feel is in my heart."

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Masvidal is stepping in to fight Usman in a highly-anticipated clash after Usman's original opponent, Gilbert Burns, tested positive for COVID-19. The original plan for Usman's title defense was a bout with Masvidal, but the welterweight star and the UFC could not agree on financial terms, leading to a tense situation until Burns' removal provided incentive for the two sides to work together.