Prass suffered a cut to his ear and some glasses were broken during the attack by about 30 fans before the team boarded a flight to return to Sao Paulo after Wednesday's Group Two match in which they conceded the goal three minutes into added time.
Palmeiras said in a statement that club directors were meeting to discuss what action to take.
"Palmeiras repudiate the acts of violence which injured Fernando Prass and do not recognise the people who took part in this sad episode as supporters of the club," the club said.
Club president Paulo Nobre described the assailants as "irrational bandits and not passionate supporters."
Argentine sports daily Ole and Brazil's Glogo said the fans were mainly after Palmeiras' Chilean midfielder Jorge Valdivia, who hid in airport restrooms as hooligans fought with players and security personnel until police intervened.
Palmeiras, relegated last year to the Brazilian second division, were looking to keep pace with group leaders Libertad of Paraguay, who have seven points from three matches after Wednesday's 2-2 draw with Peru's Sporting Cristal in Asuncion.
At the halfway stage in the group phase, Cristal are second with four points while Palmeiras, Libertadores Cup winners in 1999, and Tigre have three points each.
