Last month, Mr Key said he had received an assurance from Mr Whitney that he had not had any dealings with Mossack Fonseca, which has played a major role in tax haven activity.
Asked this morning whether he was confident that Mr Whitney had not broken this assurance, he said: "Totally. I haven't gone through all of the papers but looking at the media reporting it seems to be they are reporting some very tenuous little association between a range of New Zealanders.
"I don't think anyone should jump to conclusions because someone is a director or trustee of some company in New Zealand that through a massive association has somehow dealt with Mossack Fonseca that they have done something wrong."
When Mr Key was pressed by reporters about Mr Whitney's apparent links to Mossack Fonseca, he said: "There is nothing there I am concerned about."
Labour leader Andrew Little said the lawyer's association with Mossack Fonseca was a "new revelation".
"What it all does highlight is that there is an industry burgeoning in New Zealand which is, in reality, doing nothing for New Zealand apart from causing us ongoing international embarrassment."
Foreign trusts had "proliferated" while National was in power, he said, and were too secretive.
Soon after the Panama Papers emerged last month, the Government launched a review of the disclosure rules for offshore trusts, which could lead to less secrecy around the trust's beneficiaries and any assets held within them.
Mr Little wants the rules to be tightened further and has committed to shutting down some foreign trusts.
"I see no purpose in having foreign trusts that allow the world's mega-wealthy to put income-generating assets under a veil of secrecy here and to pay no tax in their home countries," he told reporters this morning.
"We have nothing to gain from that."
Mr Whitney is part of a lobby group which urged the Government not to tighten the rules for foreign trusts based in New Zealand in 2014.
The Revenue Minister at the time, Todd McClay, dropped the Inland Revenue Department's (IRD) proposed review of foreign trusts in 2015, saying it was not a Government priority.
It was revealed today that four other law firms in the foreign trusts lobby group had links to Mossack Fonseca.
Mr Key reiterated that the Government was not swayed by the lobby group in deciding not to proceed with a review of offshore trusts.
"People come and talk to the Government all the time about a range of issues, they make representations ... in select committees, they do it privately.
"If it didn't happen, the Government would be deeply worried that New Zealand would be making a lot of laws without engagement with the industry."
The database published today could also reveal whether any New Zealanders are hiding their assets or money in trusts overseas.
The IRD has assembled a team to pore over the database.
"If there really are some New Zealanders that have done something that is inappropriate ... they are going to get a knock on the door from IRD," Mr Key said.
Tax evasion was a very serious offence, he said, and could result in a jail sentence.
