Scott Morrison has personally spoken to Defence Minister Linda Reynolds' doctor about her extended medical leave.
Senator Reynolds has taken leave until at least April 2 as she faces intense scrutiny over her handling of rape allegations raised by former staffer Brittany Higgins.
The prime minister described her condition as "quite serious".
"I have, at the minister's permission, spoken to her doctor about this issue and it is a serious issue," Mr Morrison told reporters in Sydney on Tuesday.
"And so we are supporting her in getting the physical health treatment that she needs over this period, that doctors have advised that she needs to take."
Attorney-General Christian Porter has also taken indefinite leave after being accused of an historical rape allegation, meaning two of the eight national security committee members are absent.
Mr Morrison said both ministers were being temporarily replaced by highly competent cabinet colleagues, and he was also maintaining "a very close watch" over their portfolios.
