Mr Key said National may reach out to NZ First with the offer of a memorandum of understanding, but conceded that it was "probably not likely".
"I think more likely issue by issue we'll start trying to talk to them."
With regard to the Green party, Mr Key said; "the problem is really not so much us ruling them out, it's been them ruling us out".
A previous memorandum of understanding had worked well with the party's home insulation scheme, he said.
Later appearing on TV3's Firstline, Mr Key said Judith Collins wouldn't be a member of Cabinet any time in the near future.
"We need to go through that professional inquiry undertaken by Justice Chisholm, he'll look thoroughly at that, so, she won't be a member of Cabinet in the short term."