Mr Groser, a former diplomat turned politician, confirmed he had spoken to Paula Rebstock who is conducting an inquiry into leaks including a cabinet paper to Labour MP Phil Goff.
It had been "a preliminary discussion about two or three months ago," he told the Dominion Post yesterday.
Mr McCully said "I don't think you can convict someone for disagreeing with the contents of the MFAT change proposal."
Mr Goff has refused to confirm that he does not know the source of his leaks but the Herald has reliably been told he does not know.
His refusal to confirm he doesn't know, may well cast greater suspicion on Mr Groser along with the implication he has privately opposing the restructuring.
Mr Goff says Mr Groser risked dismissal from Cabinet for a breach of the cabinet rules of collective responsibility.
"I don't blame Mr Groser for speaking out," Mr Goff said in a statement today. "He spent a lifetime working for Foreign Affairs and knew how counterproductive and stupid Mr McCully's reform plans were."
He said Mr Groser had wrote the cabinet paper executing a u-turn on the worst aspects of the proposals.
Mr McCully denied any suggestion that he had prevented his own staff from speaking to the inquiry.
"Full co-operation has been offered and anything she has sought would have been given."
Asked if he had any idea who leaked documents to Mr Goff.
"This is a quasi-judicial process where suspicion does not have the same standing as proof."
Both he and Mr Key said they had not sought reassurances from their staff because they both trusted them and did not believe they had leaked documents.
The State Services Commissioner commissioned the Rebstock inquiry.