David Cameron defended Sarah Teather on Wednesday after the Liberal Democrat minister failed to turn up to vote with the government on the Welfare Reform Bill.
During PMQs he was asked by Tory backbencher Peter Bone why Teather was "still a government minister," saying: "On occasion I have spoken against the Government...but I am not a minister."
Earlier, Bone was quoted in the Daily Mail asking: "Why is she still in her job if she can't support Government policy?"
But the prime minister told MPs: "She supports government policy as all government ministers do."
The education minister was absent from last Wednesday's debate on welfare, where MPs voted down Lords amendments on the Bill.
Teather had previously spoken out about the "serious issues" with welfare reform.
Despite the debate having a three-line whip, a Number 10 spokesperson said Teather was "away on government business" on Wednesday morning.
"On the particular vote, there was overwhelming support for the cap, so there was no need for her to be recalled.
"The fact that she wasn't going to be able to make a vote was cleared and agreed through the usual channels."