Linda Reynolds -- who is currently embroiled in an investigation into the alleged rape of a young staffer by a colleague in her parliamentary office -- is being treated for a "pre-existing medical condition" her ministry said.

"As a precautionary measure, minister Reynolds has this morning been admitted to a Canberra Hospital," the statement read, adding she "will take a period of medical leave".

Reynolds had been due to answer questions from journalists at the National Press Club later Wednesday, at the same time the young staffer, Brittany Higgins, is due to make a formal complaint to police.

Questions have been raised about whether Reynolds responded properly to the alleged assault, with some critics calling on her to resign.

Health Minister Greg Hunt rejected suggestions Reynolds is ducking public scrutiny, saying she had been "desperate" to make the appearance but was forced to make a "reluctant decision not to do it".

Reynolds is also at the centre of fraught negotiations with French submarine maker Naval, as Australia tries to move more production onshore.

The group's CEO Pierre Eric Pommellet is currently in Australia to discuss the next step in one of Australia's largest-ever defence deals.

Shadow minister for defence Brendan O'Connor said there were "serious questions about the competency of the minister", claiming she misled parliament about the response to the rape allegations and had taken her eye off the ball.

"She needs to focus on this major contract, this critical contract for our national security," he told Sky News.

Foreign minister Marise Payne will take up the defence portfolio on an interim basis.