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.
"Now he scratches and he bites" the club said on their website.
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."
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.
