Medel, a dogged midfield terrier, scored both goals to give Boca a 2-0 victory and earn idol status from the Boca faithful at their packed Bombonera ground last Thursday.
He also had a finger bitten in an incident with River captain Marcelo "Babyface" Gallardo and was sent off when his overzealous tackling earned him a second yellow card in the 75th minute.
"A bite on the right index finger," was the Boca Juniors doctor's report.
When the two players squared up to each other on the pitch during the second half, Medel pointed his finger at Gallardo, who reacted with a quick bite that left a small gash.
"Now he scratches and he bites" the club said on their website.
There is no love lost between the two rivals and Gallardo was involved in a previous incident when he slapped former Boca goalkeeper Roberto Abbondanzieri, leaving scratch marks on his cheek, during a Libertadores Cup match in 2004.
Medel, who refused to talk about the incident as he left the Bombonera with the finger bandaged, was quoted by Boca as saying "I'm not a grass."
Gallardo, a 34-year-old former Monaco and Argentina midfielder who had scored with free-kicks in the previous two Superclasicos, had a poor 300th game for River with reports saying it could have been his last clash with Boca.
Medel was praised on both sides of the Andes and Chilean media recalled his two-goal performance for his former club Universidad Catolica against arch-rivals Universidad de Chile in a 2007 Santiago derby.
Argentina coach Diego Maradona, who watched the match from his box at the Bombonera, said: "If Medel was Argentine I'd be picking him for the national team."
Medel is a key player in Chile coach Marcelo Bielsa's World Cup team. Chile meet favourites Spain, Switzerland and Honduras in Group H at the finals in South Africa starting on June 11.
