Earlier on Tuesday, world football players’ union Fifpro had called for Muntari’s punishment to be rescinded – though it was then unaware the player had been given a second yellow card and sent off.
He was booked for dissent after asking the referee to stop Sunday’s Serie A match against Cagliari, claiming he was being racially abused.
The 32-year-old ex-Ghana international then walked off the pitch in protest – for which he received a second yellow card, officials have now confirmed.
They added not enough fans took part in the abuse to trigger action.
The Serie A disciplinary committee agreed their actions were “deplorable” but said its guidelines meant it could not impose sanctions as only “approximately 10” supporters were involved – fewer than 1% of the Cagliari supporters in the ground,
“Muntari was well within his rights to approach the referee,” said a Fifpro statement.
“Players should feel comfortable bringing any issue to the attention of the referee, especially one as significant as allegations of racism in the workplace.
“We urge Italian authorities to hear Muntari’s version of events, investigate why the situation was mismanaged, and take firm action to ensure this never happens again.”
Ex-Portsmouth and Sunderland player Muntari was playing for AC Milan when then team-mate Kevin-Prince Boateng walked off the pitch because of racist chanting during a friendly with lower-league side Pro Patria in January 2013.
Boateng has since tweeted his support to Muntari, saying he is “so proud” of his former team-mate.
Meanwhile the Serie A committee warned Lazio and Inter Milan faced partial stadium closures if there was a repeat of recent racist behaviour shown by their fans.
Napoli defender Kalidou Koulibaly suffered abuse from Inter fans while Lazio supporters targeted Roma defender Antonio Ruediger.