Sparta Prague hit out at "xenophobic" reports that said Rangers midfielder Glen Kamara was targeted by sections of a crowd comprising mainly schoolchildren during Thursday's 1-0 Europa League home win.
In March, Finland's Kamara had complained of being racially abused by Slavia Prague's Ondrej Kudela during a Europa League tie and the continent's soccer governing body UEFA banned the Czech defender for 10 games.
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.
It later decided to allow 10,000 children 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.
"It is absolutely unbelievable that after a match we have to watch innocent children being attacked and face unfounded accusations of racism," the Czech club said in a statement.
"Insulting children on the internet and in the media is unacceptable, desperate and ridiculous.
"Stop attacking our children! Our club will proudly defend our children -- our future and our pride. Slandering children on the internet is extremely cowardly."
Rangers manager Steven Gerrard initially said after the game that he was not aware of the booing but said on Friday that he heard it when he watched the game again.
"I'm fully aware now, having watched the game back with audio on. I'm actually surprised that I wasn't aware of it during the game," Gerrard was quoted as saying by Sky Sports.
"I have spoken to Glen Kamara, that conversation will remain private. Glen's okay, I'm sure he's disappointed, just like myself.
"I've been told that Rangers are going to take it up with UEFA. I think those wheels are already in motion. I'll certainly be pushing to make sure that's the case."