Aberdeen claim striker Pape Habib Guèye was racially abused during his sides draw with Greek side PAOK.
The club released a statement shortly after the full-time whistle saying that they have informed UEFA of the incident, although it's since been denied by the home club.
A club statement from Aberdeen said: "During the second half of this evening’s UEFA Conference League match against PAOK it was brought to our attention that an Aberdeen FC player, Pape Habib Guèye, was the victim of racial abuse from a section of PAOK supporters.
"Aberdeen FC club staff immediately informed the UEFA Venue Director and following conclusion of the match met with the UEFA Match Delegate to officially report the matter.
"Pape has the unwavering support of his teammates and all at Aberdeen FC will liaise fully with UEFA during the course of their investigations into this very serious matter.
"As a club we have zero tolerance for any form of discrimination or racist abuse. There is no place for such behaviour in football, or society as a whole."
In response, PAOK say the complaint is "clearly a product of imagination, as it did not come to the attention of any official".
They said no racist behaviour would be tolerated at the stadium, and there's never been any.
The club also criticised "the defiant behaviour of the Aberdeen substitutes in their equaliser", after a number of Aberdeen players appeared to approach fans following the alleged abuse.
Earlier in the evening, Duk had given the Dons an early lead before PAOK goals either side of half-time put the hosts in the ascendency.
Jamie McGrath's free-kick ensured a point for Aberdeen, though it wasn't enough to give them a shot at the knock-out stages.
A trip to Helsinki later this month awaits the Red Army, before German giants Eintracht Frankfurt grace Pittodrie in December, three days before the Viaplay Cup Final.