Senator Reynolds has set a date to return to her job on April 2, which is Good Friday, but some of her colleagues expect her to resign.

Candidates to replace her include Home Affairs Minister Peter Dutton and Government Services Minister Stuart Robert, a close friend of Mr Morrison.

While former SAS soldier and Western Australian Liberal Andrew Hastie was made Assistant Minister for Defence last December, he does not have full ministerial rank.

Another option would be to promote the Minister for Defence Industry, Melissa Price, but Mr Morrison demoted her from cabinet in his first reshuffle after the last election because of her poor performance as Environment Minister.

Mr Porter could keep the industrial relations portfolio and his cabinet rank while stepping down as Attorney-General, given concerns about any conflict of interest in his legal duties while he takes the ABC to court.

Cabinet ministers with the law degrees necessary to be Attorney-General include Communications Minister Paul Fletcher, Health Minister Greg Hunt, Employment Minister Michaelia Cash, Education Minister Alan Tudge and Energy Minister Angus Taylor.