Michael Martin had backed the Laois/Offaly TD Yesterday Afternoon.
The Taoseach's set to appoint a new Agriculture Minister today, after Barry Cowen was sacked last night.
It followed Mr Cowen's refusal to provide further public statements on allegations he attempted to avoid a garda checkpoint in 2016.
He admitted he was caught drink driving, but strongly denies trying to evade gardaí.
In a statement, the Offaly TD says the decision to sack him was surprising and disappointing.
Sinn Féin's Health spokesman David Cullinane says the Taoiseach needs to fully explain why his position flipped yesterday: