Micheál Martin said Varadkar sharing contract "was not best practice"
"The manner in which that document was sent was inappropriate."
The Taoiseach has said that Leo Varadkar's passing of a document to the National Association of General Practitioners last year was "not best practice".
Micheál Martin said the agreement should have been public knowledge "much earlier".
Speaking on Monday, Martin said: "The manner in which that document was sent was inappropriate, and I think it was not best practice.
"There was no financial gain for anyone... There was no material advantage to any person. It was not best practice, it was not appropriate to do it in that way."
Martin then mistakenly referred to Varadkar as the Taoiseach, and said that he will answer questions in the Dáil tomorrow "comprehensively", and that he will make an official statement on it.
Over the weekend, an article in the Village magazine alleges that Varadkar passed on a "confidential" agreement agreed with the IMO to Doctor Maitiú Ó Tuathail, who was the head of the NAGP.
Varadkar has also admitted that what he did was "not best practice", but that he shared no confidential or sensitive information.
In a statement on Sunday, Fine Gael said: "The Tánaiste accepts that the provision of the Agreement by an informal communication channel to the President of the NAGP was not best practice and he regrets that he did not ensure that it was provided in a more appropriately formal manner.
"There was however, nothing in any way unlawful about the provision of the Agreement to the President of the NAGP."
Since then, a number of politicians have called on the Tánaiste to further explain his actions.