Bernard Hopkins suffered defeat in his final fight after the 51-year-old was knocked out of the ring in the eighth round by Joe Smith Jr.
A flurry of punches sent Hopkins through the ropes and, after he failed to return to the ring in 20 seconds, he was beaten by technical knockout.
Hopkins said he was “shoved” and hit his head in his fall in the light heavyweight bout.
He added he twisted his ankle and “couldn’t stand up”.
Hopkins confirmed the fight would be the last of his 28-year career, which he ended with a record of 55 wins (32 KOs), eight defeats, and two draws.
The former two-weight world champion defended his world middleweight title 20 times between 1995 and 2005 and is the oldest man to hold a world title, aged 49.
The American had never been beaten inside the distance before his defeat by compatriot Smith Jr in his first fight since losing on points to Russia’s Sergey Kovalev two years ago.