Merseyside Police have helped Liverpool identify the culprit responsible for a banner of Divock Origi branded "offensive" and "racist".
The force say local police in Belgium are now investigating after the image was displayed in the away end at the Champions League group win at Genk on Wednesday, while UEFA awaits a report from anti-racism group FARE.
It has since emerged that the same banner - also condemned by Liverpool fan group Spirit of Shankly - was on display among hundreds of others in the Liverpool end at last season's Champions League final in Madrid.
Whether the banner is deemed merely "offensive" or in fact "racist" will prove crucial towards any sanctions UEFA decides to impose, with penalties for the latter being considerably stronger.
Liverpool were infuriated by the image and immediately set about having it removed on the night, branding it "completely unacceptable".
"Liverpool Football Club condemns the offensive banner displayed in our section of the ground, prior to kick-off," they said. "To be clear, the image used perpetuated a racist stereotype. This is completely unacceptable.
"We acted swiftly to have the banner removed and we are now working with the local authorities and stadium team in Genk to identify those responsible. Any subsequent action will be taken in keeping with our sanctions process."
Fan group Spirit of Shankly added: "We oppose all forms of racism. We have seen the club have taken swift action in the removal of this offensive banner, which perpetuates racial stereotyping.
"Football isn't separate from society it's part of society and we have a responsibility in ensuring people understand that there is no room for racism. Simply banning people is not the answer. Education and reaffirming there is no place in society for discrimination has to form part of the solution."
Merseyside Police said: "We can confirm Merseyside Police officers assisting local police at the Genk v Liverpool fixture on Wednesday night (October 23) removed a banner in the Liverpool supporters section.
"We worked with Liverpool FC and the local authorities to identify the person responsible, and the local police in Belgium are now conducting an investigation."