In a fiery match at the Emirates Stadium in London, referee Martin Atkinson produced seven yellow cards and awarded 47 free-kicks for fouls but the English official missed Medel stepping on Neymar in the first half.
After fouling Neymar, Medel stood up while stepping on the Brazilian striker's lower left leg, which left the 23-year-old writhing in pain.
Neymar described it as a move out of UFC, while demanding that Copa America referees defend him when the South American tournament starts in June, as he "cannot do anything".
The Barcelona star was forced to miss Brazil's World Cup semi-final last year after Juan Zuniga kneed him in the back in another feisty game, breaking one of Neymar's vertebrae.
"I hope [Copa America referees will be more aware], because I cannot defend myself, I cannot fight back, I cannot do anything," Neymar said in London.
"[If] we have a referee on the pitch that is there to punish them, then they have to keep an eye on it.
"I have to congratulate the referee [Atkinson] for the match but I think he missed in this incident."
Neymar could not believe that neither Atkinson nor any of the other three match officials saw Medel step on him.
"That wasn't part of the game because if it was, then the sport name had to be UFC and not football," he said.
"But the referee didn't see that. He's there to see everything but he [is] just not seeing. Has four referees on the pitch and nobody saw anything.
"But I know it happens, someone has to pay and I suffer the pain."
Brazil attacking midfielder Roberto Firmino scored in the 71st minute to secure a 1-0 win over Chile.
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