Colleagues of RTÉ's Martina Fitzgerald said it was initially believed newly appointed political correspondent Paul Cunningham would be working alongside her.
Mr Cunningham was already a correspondent and adding him to the political team would not have cost extra in terms of salary, one newsroom colleague told the Irish Independent.
Mr Cunningham was appointed political correspondent following an open competition for the role.
The role of political correspondent is re-advertised every five years - but RTÉ News colleagues have expressed surprise that Ms Fitzgerald lost out.
"Everyone feels for Paul too, and the thoughts were that he was going to bolster the political team. I don't think it would actually cost RTÉ anything to add him to the team. Paul has been a correspondent and would have maintained that salary," they said.
RTÉ released a statement last Friday announcing Mr Cunningham's appointment as political correspondent. The statement did not mention Ms Fitzgerald.
When quizzed on Ms Fitzgerald's role, a spokesperson for RTÉ told the Irish Independent Ms Fitzgerald would continue working as a reporter for the RTÉ newsroom.
Mr Cunningham is a highly regarded and award-winning journalist who has worked at RTÉ for 25 years. He previously held the positions of environment and Europe correspondent.
It is unclear if Ms Fitzgerald left the role with immediate effect, or whether there is a time frame to be worked out before Mr Cunningham takes over.
It is understood Ms Fitzgerald is taking legal advice.