A man who was hurt during violent clashes between fans during Belgrano's match with Talleres Cordoba has died.
Emanuel Balbo was left in a coma in hospital after he was set upon by a group of supporters during the derby match at Estadio Mario Alberto Kempes, according to local media reports.
Broadcaster footage showed the man rushing down the stand to avoid being attacked, before he falls over the edge of the tier onto a concrete staircase.
Another fan, Diego Frydman, was also hurt in an unrelated incident, the club said after the match.
"Club Atletico Belgrano is profoundly saddened by the death of Emanuel Balbo," Belgrano said on Monday, describing the news as "a very sad day for the whole sky blue family".
Belgrano called on fans to show "reflection and peace" as they promised to work with authorities "in order for justice to be done for Emanuel".
"This is not about giving effective speeches here, but about in-depth action in the corresponding area," they added. "That is the real and true commitment of this club.
"Our condolences to the family and friends. Rest in peace, Emanuel."
The Argentine Football Association (AFA) condemned the incident and vowed to work with authorities to locate the perpetrators.
"The Argentine Football Association joins with the family of Emanuel Balbo in this difficult and painful moment and strongly condemns the criminal action that occurred in the game between Belgrano and Talleres de Cordoba," it said in a statement.
"This house rejects all these actions, which are those of criminals who deal so much damage to society as a whole and particularly to the footballing family.
"We will offer all possible collaboration with the security services to determine those responsible for this inconceivable aggression, articulating the necessary measures to ensure that incidents such as this do not ever happen again in any Argentine football stadium."
The match between the local rivals finished 1-1, leaving Belgrano second-from-bottom of Argentina's top tier.