She was due to debate with Simon Harris tonight
The spokesperson for the Love Both group, Cora Sherlock, pulled out of the penultimate debate on the Eighth Amendment referendum just hours before it went to air.
She was due to debate with the Health Minister Simon Harris on Prime Time tonight, after accusing him of hiding from debating the issue last week.
It is understood Maria Steen of the Iona Institute was originally put forward as a replacement for her.
However RTÉ resisted, as Ms Steen also featured in a TV debate on the issue last week.
Instead, it will just be a two-way debate with Mr Harris and Sinn Féin's Peadar Tóibín - with Ms Sherlock not being replaced.
The programme is taking place in front of a studio audience, with Miriam O'Callaghan and David McCullagh as moderators.