Tigre have accused police of pulling guns on their players at half-time in the second leg of their Copa Sudamericana final at Sao Paulo.
The Argentinian club's players refused to come back out onto the pitch for the second half of the match, with Sao Paulo declared the winners of the tournament.
Tigre claimed they had been attacked by around 20 men in the dressing room following a brawl involving players and officials as the teams left the pitch at half-time.
"They pulled two guns on us, the rest of the match is not going to be played," Nestor Gorosito, the Tigre coach, told Fox Sports at the stadium.
"They ambushed us and one of them pulled out a revolver and put it against [goalkeeper] Damian Albil's chest. Their security and police also hit us. There were around 20 of them."
Media reports in Argentina showed photographs of bloodstains in the dressing room, and players claimed they had been hit.
But the Sao Paulo goalkeeper Rogerio Ceni said: "They [Tigre] came here to fight, not to play. We are not worried. I don't know what happened inside the dressing room."
Referee Enrique Osses declared Sao Paulo champions, despite admitting that he had heard reports of a disturbance in the dressing rooms.
"We did not see anything, but we have heard some things about what happened," the official said. "We saw there were some injuries to the Tigre players, but I don't know what caused them."
Romer Osuna, a Bolivian official with CONMEBOL, said the Tigre players had been too scared to return to the pitch.
"The Tigre people declined to play because they considered security was not good enough," he told Fox Sports.
"The referee abandoned the game because it was not right to play on. This decision is final. It is a shame that a continental final finished in this fashion."
The Tigre players remained inside their dressing room for three hours as Sao Paolo celebrated after being handed the trophy.
"They were going to lose by a big score. Our biggest victory is the fact that the Argentines ran away," the Sao Paulo president, Juvenal Juvencio, told the club's official website.
Tigre have made an official complaint to police, and also said their team coach had been attacked, with stones thrown at it, as it made its way to the stadium before the match.