Simon Coveney fears his supporters in the Fine Gael leadership race face being axed from their ministerial posts by a vengeful Leo Varadkar.
Sources close to the Cork TD have complained that Mr Varadkar's team gave some ministers an ultimatum "to back him or suffer the consequences".
Mr Coveney admitted he is "concerned about the people who are committing to me".
The Housing Minister's side allege up to a dozen 'turncoats' have come out publicly for Mr Varadkar after initially promising support to their man.
And there have been claims that 'dirty tricks' were behind last-minute inquiries to Fine Gael headquarters about the possibility of Simon Harris being added to the election ticket.
The Health Minister has insisted he has no idea who would have made such call.
Mr Varadkar has the backing of 45 of Fine Gael's 73 TDs, senators and MEPs.
Meanwhile, RTÉ's managing director of news Jon Williams waded into the debate, posting a tweet in which he appeared to support Mr Varadkar.
It was later deleted, with RTÉ insisting he decided to delete it himself.
But Mr Coveney's campaign has fired a warning shot at RTÉ.