Stevenson lost his WBC light-heavyweight title to the unbeaten Ukrainian at the Videotron Centre in his native Canada after being stopped in the 11th round on Saturday night.
Adonis Stevenson is in a “critical condition” after being knocked out by Oleksandr Gvozdyk, according to his promoter Yvon Michel.
The 41-year-old, who was the oldest and longest reigning champion in boxing, was stretchered out of the ring and taken to hospital in an ambulance.
“They wish to inform friends and supporters that Adonis is currently in critical condition in intensive care at the hospital, following his fight against Oleksander Gvozdyk.
“They appreciate the concern and support of all. There will be no other comments for the moment and they respectfully ask for your understanding in their desire to stay in private.”
Stevenson was leading the fight on two of the judges’ scorecards, and drawing on the third, when he was stopped. He won the WBC title back in 2013, and defended it on 10 occasions, including against Tony Bellew that same year.