Shane Mosley could be forced to consider retirement after suffering his first stoppage defeat against Anthony Mundine in Sydney.
The 42-year-old veteran failed to come out for the seventh round after complaining of back spasms and will make a decision about his future when he returns to the US.
Mosley, a former three-weight world champion, was forced on the back foot by Mundine's early aggression in the first round.
The Australian continued to bully Mosley in the second, but 'Sugar' responded with a decent right hand in the third round.
Both fighters were hurt as they stood and traded in a thrilling fourth and Mundine piled on more powerful punches in the following two rounds.
Mosley was struggling to keep Mundine at bay and was pulled out by his corner before the seventh.
When asked whether he would fight again, the veteran said: "What's done is done."
Mundine's career is back on track after a January defeat by compatriot Daniel Geale and he paid tribute to his beaten foe.
"I was in killer mode, but my heart goes out to Shane, I know he's a winner," said the former NRL rugby league star. "He's not one to pull out for nothing. He's one of the greatest fighters to have ever lived."