Slavia Prague president Jaroslav Tvrdik is "terribly ashamed" by ultras who unveiled a racist banner targeting Rangers player Glen Kamara.
Kamara claimed he was racially abused by Ondrej Kudela during Rangers' Europa League defeat to Slavia on Thursday.
Kudela, who covered his mouth with his hand, leaned into Kamara and said something that sparked fury from the Rangers man and a nearby team-mate.
The Czech club have strenuously denied the allegations and issued a statement on Friday defending Kudela, who they allege was subjected to an attack by Kamara after the match.
Slavia also revealed they had filed a criminal complaint against Kamara for the alleged attack.
UEFA has launched an investigation into the respective incidents, including the claimed post-match altercation, which Slavia claim was "prepared and thought out, including deliberately covering the cameras at the scene of the incident".
Images of a group purporting to be Slavia ultras began circulating the day after the game, with the unidentifiable people holding a banner that named Kamara and contained a racial slur.
Tvrdik condemned these actions on his official Twitter page, writing: "I am terribly ashamed of the content of the photo published by some radical fans.
"It's absolutely disgusting, pathetic and racist. NO TO RACISM!"
In Slavia's initial statement defending Kudela, they insisted he was a "football gentleman".
Kamara released a statement of his own via a solicitor on Friday in which he called out Kudela's defence of just swearing at him as "a complete utter lie which does not stand up to any form of scrutiny".