Rangers reserve goalkeeper Grant Adam chanted a sectarian slogan outside a nightclub in Glasgow's city centre.
The 21-year-old sang "hey, hey, f*** the Pope and the IRA" in front of two police officers while on a night out in Merchant City.
Adam, whose older brother is former Rangers and current Liverpool midfielder Charlie, committed the offence in the early hours of November 6 last year.
The Scotland under-21 cap, who is currently on loan to Airdrie United, was overheard and arrested by two nearby police officers who were dealing with another matter outside the Corinthian nightclub in Ingram Street.
After hearing evidence from officers PC David Beck and PC Magnalena Ross, Sheriff John Baird ruled that Adam, of Bearsden, East Dunbartonshire, was guilty of chanting the sectarian phrase, and fined him £500. He said it was not challenged that a sectarian comment was made and in the circumstances it was a breach of the peace.
He said: "I am satisfied beyond reasonable doubt on the evidence of these two police officers it was you who made the comment. I have absolutely no doubt that I should be satisfied by the Crown case."
PC Beck told the court: "At that time the stewards had asked me to speak with a couple of people who had tried to get in but were refused entry, the stewards believe them to be too drunk to enter and at that time I had approached these two males to speak to them."
He told the court on Friday that Adam started singing: "Hey, hey, f*** the Pope and the IRA."
After the court decision, A Rangers spokesperson said: "We are aware of the outcome of the court case and the club condemns all forms of sectarianism and anti-social behaviour. An internal disciplinary process will take place and the club will make no further comment until that is complete."