Josiah Harrell, a would-be UFC debutant, will be undergoing brain surgery instead of stepping into the octagon after an MRI exam uncovered an undiagnosed illness.

The prefight MRI, which is required by the UFC and Nevada State Athletic Condition, showed that Harrell has moyamoya, a rare blood vessel disorder.

He was scheduled to fight Jack Della Maddalena at welterweight on Saturday as part of UFC 290 in Las Vegas, but had to pull out as a result of the MRI.

Maurice Blanco, Harrell’s manager, told ESPN that Harrell will undergo brain surgery, calling the MRI result “a blessing in disguise” because it would have been dangerous to continue fighting.

He added that after recovering from surgery, Harrell will return to fighting.

It took a stroke of luck for Harrell to even get the chance to be on the card Saturday.

Sean Brady was originally scheduled to fight Della Maddalena, but had to withdraw last week due to septic bursts in his left elbow.

Harrell was the replacement — taking the fight on six days’ notice while getting the opportunity over a number of UFC veterans.

Prior to this, Harrell is undefeated in seven professional fights, in Ohio, Pennsylvania and Kentucky.

He also played football and wrestled.

Blanco told ESPN that none of those jurisdictions required he get an MRI before fighting.

Harrell is not the first UFC fighter whose MRI has turned up moyamoya — in 2019, Vince Murdock suffered the same diagnosis under similar circumstances.

He went on to make a full recovery and return to the octagon.

Moyamoya is “caused by blocked arteries at the base of the brain,” according to the National Institute of Neurological Disorders and Stroke.

Therefore, the condition is not believed to be career-ending.

UFC 290 is scheduled to go on without Della Maddalena on the card.