On Sunday, fans of Atletico Paranaense and Vasco da Gama fought running battles in the stands at the stadium in the city of Joinville from as early as the 17th minute when Atletico took a 1-0 lead.
A police helicopter was forced to land on the pitch to bring the violence, which lasted more than one hour, to an end and allow medical help to the injured.
Four spectators were rushed to San Jose hospital in Joinville, in the southern state of Santa Catarina, but one was released shortly afterwards.
Two more were still under observation and expected to leave the hospital Monday, while the other, who is in more serious condition, was to be moved to a private clinic, the hospital said.
"He is in a more serious condition, with head trauma," a hopital spokesman said. The match was held up for an hour before being restarted. Atletico won the game 5-1.
Military police did not respond quickly because security was handled by a private security firm, a spokesman said.
The violence erupted six months before the kickoff of the World Cup as the country races against time to complete the 12 host arenas for the high-profile event,
Several stadiums, including Sao Paulo's Arena Corinthians which was hit by a fatal crane accident, will be delivered behind the initial December 31 deadline set by football's world governing body FIFA.
Joinville stadium is not hosting a match in the World Cup which starts on June 12.