Former minister Pansy Wong is not likely to return to work until a review into her use of MPs' travel allowances is complete.
Mrs Wong resigned her ministerial portfolios after admitting her husband Sammy conducted personal business during a trip to China, which is against the rules covering the use of the rebate perk for MPs and their spouses.
Speaker Lockwood Smith's office was investigating and a report was expected within three weeks. Mr Key has said Mrs Wong shouldn't comment until she had read the report.
Mrs Wong was on leave last week and Mr Key said he had not talked to her for more than a week.
He said she would remain away from Parliament this week and would return when she could answer questions.
"I don't know when she'll be due back.
"I want her to be able to answer those questions fully and with the full facts in front of her and at the moment she's unable to do that."
The media would not be happy if she could not answer questions on her return, Mr Key said.
"I'm pretty sure you'll find 'no comment' isn't acceptable to you (the media)."
Labour leader Phil Goff said Mrs Wong should front up or resign.
"She's had more than enough time to think about how much taxpayers' money she's misused to promote her husband's personal business interests.
"She's been in hiding long enough."
Mr Key did not rule out Mrs Wong returning as a minister if National won the general election next year.
Meanwhile, he was working on appointing her replacement for minister of women's and ethnic affairs.
Mana by-election candidate Hekia Parata was being touted as a strong contender, as was Selwyn MP and select committee chairwoman Amy Adams.
Mr Key said with the mine explosion in Greymouth he had not had much time to think about it but he did not rule out promoting Ms Parata.