Police have released a description of the man who is alleged to have directed racially aggravated abuse towards Kilmarnock footballer Josh Magennis.
The incident took place at 4.40pm on Saturday during the club's game against Hearts at Tynecastle Stadium in Edinburgh.
Magennis is understood to have made the allegation following his side's 1-0 defeat.
The 25-year-old is in his second season with the Ayrshire club and the striker is also a Northern Ireland international.
The man responsible is believed to have been seated in lower section E of the Wheatfield Stand.
He is described as being white, with a stocky build, aged in his mid 40s, with dark hair that is receding on top.
He was wearing dark glasses and a dark jacket that possibly had red lining.
Pc Gavin Stupart said: "Racial abuse is absolutely unacceptable, in any circumstances.
"The behaviour of the majority of fans at Tynecastle on Saturday was excellent and I want to thank both clubs for their co-operation.
"We're conducting various inquiries in an effort to trace the perpetrator and I'd ask any witnesses to this abuse, or anyone who recognises the description of the suspect, to come forward."
Hearts said in a statement on Saturday: ''The club can confirm that following this afternoon's game, a complaint was made to Police Scotland by a Kilmarnock player.
''The Kilmarnock player alleges that an abusive comment was made relating to his nationality by an individual seated within the home end at Tynecastle.
''The alleged abusive remark related to the player being Irish. The player is from Northern Ireland. To clarify, this allegation does not involve the player's colour, religion or sexuality.
''Senior figures from both clubs were present when the player made the complaint and discussed the matter fully thereafter.
''Heart of Midlothian FC has a number of players of different nationality playing in the current squad and is very proud of the international make-up of our team.
''We will fully support any police investigation into reports of abuse such as the one which has been reported today.''