"Stefan Struve blacked out in the locker room," UFC President Dana White tweeted from the official SportsCenter account. "He has elevated heart rate and is out of the fight. I'd never risk his health.
"His heart rate was up, and he blacked out," White subsequently told MMAFighting.com. "They think it was a panic attack, but didn't want to take any chances."
White added that Struve was hyperventilating.
Struve was expected to challenge Mitrione in his first fight since the discovery of a leaking aortic valve and an enlarged heart in August 2013. After undergoing treatment to lower his blood pressure and minimize his blood leakage, the 26-year-old was initially cleared to return by a doctor in Holland, as well as the UFC's official doctor, however Saturday night's episode has now put that return on hold.
"Stefan had some conditions where he had some palpitations, his heart felt like it was moving quick," Dr. Jeffery Davidson explained on the broadcast. "The team evaluated him, they called in a medical group -- myself and a couple other doctors -- we took a look at him. Stefan had a near-fainting spell. He's doing great right now, that's the most important thing. He's safe and he's healthy right now. We are monitoring him for precaution. But on the consult of the group and the medical doctors on staff, I think we're going to tell him, obviously, no fighting today.
"Stefan's condition is very stable. We'll have to look at him in the future. He can fight another day if he'd like to. Medically he's going to do well. We're going to take precaution tonight."