UEFA have opened disciplinary proceedings into "potential discriminatory incidents" during Rangers' 1-0 Europa League defeat at Sparta Prague last week, European soccer's governing body said in a statement on Tuesday.
Rangers midfielder Glen Kamara was jeered throughout Thursday's game at the Letna Stadium, which UEFA had initially ordered closed for the match after Sparta supporters had racially abused Monaco's Aurelien Tchouameni in a Champions League qualifier.
UEFA later decided to allow 10,000 schoolchildren to attend the game against the Scottish champions.
The jeering reached its peak in the second half when Kamara was sent off, media reports said.
Sparta Prague said on Friday that the allegations were unfounded, while Czech Foreign Minister Jakub Kulhanek has summoned Britain's ambassador to discuss the issue.
Rangers manager Steven Gerrard called for harsher sanctions against the club while Kamara's lawyer Aamer Anwar said Kulhanek's government should use the opportunity to "address the deep rooted racism that exists in their country".
In March, Finland's Kamara had complained of being racially abused by Slavia Prague's Ondrej Kudela during Rangers' Europa League tie and UEFA banned the Czech defender for 10 games.
(Reporting by Hritika Sharma in Bengaluru; Editing by Ken Ferris)