Former RTÉ GAA pundit Joe Brolly has launched legal action against the broadcaster.
It is understood papers were lodged at the High Court in Dublin on Thursday.
A spokesman for the Irish Courts Service last night said "the basis of the claim is defamation".
He is being represented by Rennick Solicitors, which has offices in Meath and Dublin.
Details of the case were not known last night
A barrister by profession, Mr Brolly helped Derry to their first and only All-Ireland football title in 1993.
He later worked as a GAA pundit and for years was a regular face on RTÉ's The Sunday Game until 2019.
In March this year there was controversy after RTÉ muted him during a live debate about a united Ireland.
The Dungiven native was silenced as he launched a broadside against the DUP, whose MP Gregory Campbell had earlier taken part in the programme hosted by Claire Byrne.
Mr Brolly was cut off after accusing the DUP of being homophobic and racist.
“You see them chuckling and guffawing when people are trying to have a serious discussion," he said, speaking from a studio in Belfast.
"Laughing at the Irish language, laughing at Gaelic sports, the homophobia, the racism, all these things.”
During an exchange Brolly was asked to refrain from making accusations against the DUP, as Mr Campbell was no longer available to respond.
Ms Byrne asked for his video link to be removed from the screen when Mr Brolly asked: “Which ones would he deny?”,
Mr Brolly later defended his comments and described RTÉ as being "like North Korea".
Mr Brolly could not be reached for comment last night.
