Argentina playmaker Juan Roman Riquelme could face charges of inciting disorder after an angry goal celebration in Boca Juniors' 2-1 win over Racing Club.
Public prosecutor Luis Cevasco told the TN cable news channel he was studying Sunday's incident when Riquelme ran 50 metres to point his finger at a supporter.
"In principle he has violated two rules," Cevasco said on Monday. "One which concerns affecting the progress of the match and another which concerns inciting disorder.
"We have to verify the motive and the gestures," he said, adding the offences could yield fines or up to 10 days in custody.
Early in the second half Riquelme appeared to be involved in an altercation with the supporter who was sitting only metres from the touchline in Boca's tightly-packed Bombonera stadium.
After volleying the winner on the hour the player ran half the length of the pitch and pointed at the fan who was then pushed by several other supporters, leading to a scuffle.
"I didn't do anything bad," Riquelme said in a television interview. "I just shouted when my team scored a goal. There are people who pay to get in and think they can insult us for two hours."
"So many things go on in this country and I think it's daft to talk about this matter."
In a separate interview with the same channel, the fan Agustin Pozzetti, 21, said he had simply shouted words of encouragement to Riquelme.
The playmaker returned to former club Boca this year after being sidelined by Spanish club Villarreal following a long-running row.
Riquelme helped Argentina win the gold medal at the Beijing Olympics in August, taking part as one of three permitted over-age players in the under-23 event, but looked lethargic after returning home.
In October he was involved in a public row with Julio Cesar Caceres, who said his team mate appeared tired and showed more motivation when playing for his country.