President Obama warned those at the meeting that the campaign against Isis would be drawn out and Mr Key said "he might be right about that in terms of their strength".
"Re resolve of Isis to rain carnage on the world is obvious for everyone to see. So these things are never resolved quickly."
He said New Zealand was already providing humanitarian support and "that might be the option that we decide to deploy".
Labour MP Phil Goff's claim the Government had already effectively committed to the fight against Isis was "a very crazy sort of notion".
Mr Key still planned to sit down with other parties and give them confidential briefings on New Zealand's potential deployment, "and we hope that they'll support whatever decisions we ultimately make but we haven't made any decisions yet".
Mr Key said Defence Force had again assured him that the meeting at Andrews Airforce Base near Washington of 22 international defence bosses was "a regular meeting".
He wasn't sure the Defence Force had known that President Obama would be attending and he wasn't informed of that either.
Yesterday Mr Key said he understood that Isis and coalition efforts to combat it were "not the purpose of the meeting" but would be discussed as one item on the agenda.
This morning he had changed his tune saying: "This meeting has a focus on Isis but I'm sure it discusses other things as well".