Around 40 Flamengo fans have been detained after setting off firecrackers outside a Rio de Janeiro hotel in which they believed members of rival team Independiente staying.
Flamengo play the Argentine side in the second leg of the Copa Sudamericana final at the Maracana Stadium on Wednesday.
Rio's Public Security Department said Flamengo fans shouted insults, sang songs and lit firecrackers outside the Hilton Hotel on Copacabana beach in the early hours of Wednesday.
Police used tear gas to bring the crowd under control.
CONMEBOL, South American football's governing body, condemned the violence in a statement on Twitter.