"It is with complete devastation that we have to announce that after a week of battling for his life John Cooney has sadly passed away," Mark Dunlop of MHD Promotions said on social media.
The 28-year-old had been in hospital in Belfast after surgery.
He had left the ring on a stretcher after last Saturday's fight at the city's Ulster Hall was stopped in the ninth round.
"Such a tragedy to lose this fine young boxer," said former featherweight world champion Barry McGuigan.