Borussia Dortmund have condemned alleged racist chants from Atalanta fans as "completely unacceptable" after Michy Batshuayi claimed he was subjected to them during Thursday's Europa League clash.
The Belgium international, on loan from Chelsea, wrote on Twitter that fans at Reggio Emilia's Mapei Stadium made monkey noises during the 1-1 draw.
"We fully support his words," a Dortmund spokesperson told ESPN FC. "Such behaviour is completely unacceptable, in football stadiums as much as in all other areas of life."
Meanwhile, a UEFA spokesperson told ESPN FC they were "in the process of gathering information and reviewing the official's reports," regarding the matter.
Batshuayi played the entire 90 minutes as substitute Marcel Schmelzer's 82nd-minute equaliser sent Dortmund into the round of 16 with a 4-3 aggregate victory.
Atalanta received a one-game stand closure last month that was suspended for one year after Napoli defender Kalidou Koulibaly was subjected to racist chants during a Serie A clash.
Told about Batshuayi's tweet after the game, Atalanta president Antonio Percassi told Sky Sports: "I'll be honest, I didn't hear them.
"If they did happen, then I am very sad and absolutely apologise to Batshuayi. This should never happen."
Information from the Press Association was used in this report.