Celtic have refused to comment on a report that two players were captured on an amateur video featuring sectarian chants.
Scotland international Stephen Pearson appears on the clip, which was apparently filmed at a function attended by players and fans.
Welsh striker John Hartson is also on the video, according to the Press and Journal newspaper.
The grainy footage, which has been widely distributed on the Internet, shows Pearson and what is said to be Hartson with three fans on a stage during a boisterous singalong.
The Irish folk tune Fields of Athenry is being sung, punctuated by shouts of 'IRA' and 'Sinn Fein'.
A man resembling 30-year-old Hartson, dressed in a black suit and shirt, hugs a fan just before the crowd belts out another 'IRA'.
The five on the stage are cheered on by figures in the background.
Pearson's agent today confirmed the 23-year-old midfielder featured on the clip but strongly denied that he had joined in any sectarian shouts.
Willie McKay told the Scottish Press Association: 'Stephen's seen the video and he said he sang Fields of Athenry, but he never shouted 'IRA'.
'This song is sung at Celtic games and at supporters' nights every week, there's nothing sectarian about the Fields of Athenry. I can assure you that Stephen is not sectarian at all.'
Hartson's agent, Jonathan Barnett, dismissed the newspaper report as 'complete rubbish'.
Glasgow-based Celtic, which has won plaudits from Scotland's First Minister Jack McConnell for their campaign to stamp out bigotry, refused to comment.
Celtic manager Gordon Strachan was questioned about the newspaper report at his weekly press conference today.
He said: 'I have not seen it. I have no comment to make.'
It is not clear where or when the video, which has been viewed by thousands of people on the Internet, was filmed.
Fields of Athenry - a ballad about the 1840s Irish famine, rebellion and prison ships - has become an unofficial anthem for the Parkhead faithful.
The Bank of Scotland Premier League leaders play Clyde on Sunday in the Tennent's Scottish Cup third-round tie, after which the First Minister is due to make the draw for the next round.
New signing Roy Keane, formerly of Manchester United, will make his debut for the Hoops at the game.
The vice-chairman of Celtic's Old Firm rivals Rangers, Donald Findlay, quit in 1999 after he was filmed singing a sectarian song at a social club.