Borrussia Dortmund striker Michy Batshuayi said he was racially abused by Atalanta fans during the second leg of their Europa League last-32 tie.
The Belgian, who is on loan from Premier League champions Chelsea, scored two goals in the first leg and helped Dortmund secure a 1-1 draw with Atalanta in the return leg as the German side progressed to the last 16 with a 4-3 aggregate win.
"2018 and still racists monkey noises in the stands ... really ?!," Batshuayi wrote on his official Twitter account after the match.
"Hope you have fun watching the rest of Europa League on TV while we are through #SayNoToRacism."
Atalanta hosted the match at the Mapei Stadium after their home ground, the Stadio Atleti Azzurri d'Italia, was deemed unsuitable for European competitions by UEFA.
Several Italian clubs' supporters have been accused of displaying racist behaviour towards opposition players, with Juventus' Blaise Matuidi alleging racist abuse by fans in Serie A matches against Verona and Cagliari earlier this season.
Atalanta were handed a suspended one-game stand closure after Napoli defender Kalidou Koulibaly was subjected to racist chants during a league game between the two sides.