The violence occurred in the closing minutes of Clube de Regatas Brasil's 1-0 victory over Centro Sportivo Alagoano in the final of the Alagoas state championship in the northeastern city of Maceio.
Images broadcast live on television showed a Clube de Regatas supporter being kicked and bludgeoned with an umbrella while lying motionless on the ground at the Rei Pele stadium.
"The guy is in a serious state. I'm not sure if he's going to survive," an unidentified Clube de Regatas spokesperson was quoted telling the Uol portal.
The spokesperson said another injured fan was taken to hospital suffering multiple injuries.
The names of the victims were not known and it was unclear if police made any arrests.