Ryan Burnett was forced to surrender his WBA bantamweight title after sustaining a fight-ending back injury during his World Boxing Super Series quarter-final against Nonito Donaire.
The Belfast fighter, 26, was not able to punch with his right hand during the fourth round, after which he retired.
Victory in Glasgow gave Donaire, 35, the WBA and vacant WBC diamond belt.
The Filipino four-weight world champion will face South African WBO title-holder Zolani Tete in the semi-finals.
After the third round, Burnett could be heard telling trainer Adam Booth: "I cannot move it. I cannot throw a shot."
He dropped to his knees in the next round after attempting to throw a punch, and pulled out of the fight at its conclusion.
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Fans denied a close encounter
Burnett, ahead on all three judges cards when the fight was ended, shaded the early rounds against an opponent who had not fought at 118lb for seven years.
Confident in his own upper-body movement, Burnett appeared unperturbed when cornered by Donaire and landed successful shots with consecutive left-right combinations.
The veteran Filipino, whose last fight ended in defeat by Burnett's compatriot Carl Frampton, enjoyed the better of a third round which did enough to suggest the crowd were in for a close contest.
Donaire, clearly the bigger man at bantamweight, walked down his opponent at every opportunity while Burnett, without a knockout in his past seven wins, seemed content to operate on the back foot while landing stylish combinations.
'Not the way I would like to win'
Unable to answer the bell for the fifth, Burnett was treated in the ring before leaving the SSE Hydro on a stretcher.
He will return to Belfast for further medical assessment in order to establish the extent of the injury.
WBSS promoter Kalle Sauerland said in the post-fight press conference that Burnett had slipped a disc in his back.
"As a warrior and as a fighter, Burnett is an amazing fighter," said Donaire, who immediately moved to comfort his opponent after the fight was ended.
"Early on he just kept coming at me. A win is a win and it wasn't the way I would like to win but he's an amazing fighter."
Despite entering the WBSS as number one seed in the bantamweight competition, Burnett has not only lost his existing world title but also the opportunity to become undisputed world champion, a title which will be bestowed upon the winner of the Ali Trophy.
Donaire held the WBC and WBO bantamweight titles in 2011 before eventually vacating the titles in favour of a move up to 122lb.
He will face Tete, who defeated Russian Mikhail Aloyan in their quarter-final last month, early next year.
'So sad for Ryan' - reaction
Former world cruiserweight champion Tony Bellew: "So sad to see Ryan Burnett leaving the ring like that. Donaire is a proper gentleman and a great fighter who wouldn't want to win like that. I just wish and hope for a speedy recovery for Ryan."
Bellew's trainer Dave Coldwell: "Really hope this isn't a career-threatening injury for Ryan."
Former British light-heavyweight champion Frank Buglioni: "Gutted for Burnett. He was looking fantastic. Sad ending to a great fight. Donaire showing real class with his compassion and lack of celebration."