Rangers have been handed a new disciplinary charge by UEFA after supporters engaged in sectarian chants away to Legia Warsaw last week.
The incidents occurred during the two sides' Europa League play-off first leg, and Rangers say they are liaising with UEFA regarding the charge.
Rangers have already been forced to partially close Ibrox for the second leg against Legia on Thursday after they were charged with sectarian chanting at home to St Joseph's in the Europa League last month.
Rangers have warned a further charge could lead to a full stadium closure, and have told UEFA they will not request tickets for their next European away match.
The club urged supporters to refrain from taking part in sectarian chanting, saying: "This kind of behaviour has no place at Ibrox, or anywhere else where our many teams appear.
"Offenders must please stop. You are endangering your club. Those who wish to sing offensive songs must realise by now that they are insulting Rangers players, staff, and fellow fans.
"There is nothing clever, bold or even defiant in what this small number of supporters are doing."