Joe Joyce could be forced to consider retirement after he suffered a stoppage loss to Artem Suslenkov in Moscow.
The British contender appeared to gesture that he could not continue following a crunching combination from Suslenkov and the referee waved the fight off after the Russian followed up with a flurry of punches in the 11th round.
Joyce has lost five of his last six bouts and the 40-year-old will face fresh calls for him to hang up his gloves after this latest setback on the Murat Gassiev vs Peter Kadiru undercard.
Suslenkov, who extended his unbeaten record to 15 wins, had displayed his superior hand speed in the early rounds.
Joyce attempted to sink in hurtful body shots in the third, but was badly hurt by Suslenkov in the following round.
A short, sharp right hand rocked Joyce in the fourth, leaving him on unsteady legs, although he somehow managed to withstand the assault from Suslenkov.
But Joyce's renowned toughness was eventually broken in the penultimate round as he waved his glove at Suslenkov in an apparent admission that he could not continue before the referee stepped in.
Joyce holds a stoppage victory over current WBO world champion Daniel Dubois, but following the third successive defeat of his career, the Londoner's hopes of a major title fight are surely over.
In the main event, Gassiev defended his WBA heavyweight title with a sixth-round stoppage of Peter Kadiru.
Gassiev made an aggressive start against Kadiru, who had stepped in as a late replacement for the injured Tony Yoka, and the Russian troubled his opponent with a punishing attack in the second round.
Kadiru sagged against the ropes in the sixth following more hurtful punches from Gassiev and the German's corner waved the towel to signal the ending.
Britain's Derek Chisora climbed into the ring for a post-fight head-to-head with Gassiev, fuelling speculation that he could receive a future WBA title clash against the Russian.
