Tyson, once considered one of the greatest heavyweights in the sport's history, said from his stool Saturday at Washington's MCI Center: "I don't have the guts to fight anymore. My heart is not in it anymore. I don't want to disrespect the sport I love," the Washington Post reported Sunday.
Referee Joe Cortez had stopped the fight at the urging of Tyson's corner.
At the time of Tyson's concession, two judges, Tammye Jenkins and Stephen Rados, had the heavyweight leading, 57-55, while Judge Paul Artisse had McBride winning by the same score. It was Tyson's third loss in his last four fights.
Earlier in the fight, Tyson, who was fighting for the first time since he was knocked out July 30 by Englishman Danny Williams, had reportedly attempted to break McBride's arm and then purposely head-butted the Irishman, the Post said.
McBride (33-4-1, 28 knockouts) said: "This win was for the pride of Ireland."
"I proved everyone wrong tonight."