On Thursday, the FIGC―Italy's football federation―announced the Nerazzuri will play two matches behind closed doors and that one of their stadium's stands, the Curva Nord, will be shut down for a third, per Football Italia.
Per BBC Sport, Inter have the option to appeal.
Koulibaly himself has been suspended for two matches after he was sent off for "sarcastic applause" of the referee after being booked during the game.
The Senegal international received constant abuse throughout the 1-0 loss, and Napoli manager Carlo Ancelotti said he asked the referee to suspend the match on three separate occasions, per sportswriter James Horncastle:
James Horncastle @JamesHorncastle
Ancelotti says Napoli asked for the game to be suspended on 3 occasions for racist chanting aimed at Koulibaly. Speaker read out 3 warnings. Ancelotti bewildered why game wasn’t interrupted. Adds next time Napoli will stop playing even if it means they forfeit the game
The 27-year-old took to social media after the contest:
The FIGC said they arrived at the punishment after taking into account "the aggravating circumstances related to their repetition and the climate created inside the stadium." Koulibaly has been on the receiving end of abuse before, and Juventus received a stadium ban of their own in a similar situation earlier this season, per Goal's Taiye Taiwo.
Koulibaly received support from fans and players after the match, including Cristiano Ronaldo:
The abuse from the fans wasn't the only thing that marred Wednesday's marquee clash, as violence erupted before and during the match. Four Napoli fans were stabbed before and during the encounter, while an Inter fan was killed after being hit by an SUV before the game.