UEFA have received an appeal regarding their decision to clear Rangers of sectarian chanting.
The club were found not guilty of alleged discriminatory chants during the recent Champions League tie with Villarreal.
Gerhard Kapl, who compiled the evidence for the governing body, has challenged last week's ruling.
A spokesperson for European football's governing body said: 'An appeal has been made against the disciplinary committee's decision to clear Rangers supporters of singing discriminatory songs in the first game with Villarreal.
'We cannot comment on what the UEFA delegate recommended.'
The appeal will be heard before the end of the season.
Meanwhile, the Scottish Premier League have played down reports Rangers have been cited for instances of sectarian singing during Saturday's game with Aberdeen at Ibrox.
The SPL have yet to receive the report from their match delegate Alan Dick.
But an SPL spokesman said: 'We have to wait and see what is reported to us. If these issues or areas are flagged up by the SPL then there will be discussions with clubs.
'But there is nothing new. Delegates reporting crowd behaviour is part of the remit.
'The match delegate has to report a number of issues ranging from the referee, to issues of commercial, or issues of fair play, that would cover behaviour of players, club officials and also clubs supporters.
'We have asked them to report on these matters since the initiative was introduced.'