The UK's new defence secretary is expected to be announced by Prime Minister Rishi Sunak on Thursday.
Ben Wallace, who held the role for four years, resigned on Thursday after announcing last month he would leave his post at the next cabinet reshuffle.
Names mentioned by senior Conservatives as potential replacements include Armed Forces Minister James Heappey, Chief Secretary to the Treasury John Glen and Energy Secretary Grant Shapps.
Downing Street has refused to comment on Mr Wallace's successor.
In his resignation statement, Mr Wallace said his military and political careers has come at "a personal toll to me and my family".
Mr Wallace said: "The Ministry of Defence that I leave is now more modern, better funded and more confident than the organisation I took over in 2019.
"I genuinely believe that over the next decade the world will get more insecure."
Rishi Sunak said Mr Wallace had worked in "the most demanding posts in government" and left with his "thanks and respect".
As well as Mr Heappey and Mr Glen, there are reports that a Tory MP who has done the job before may be asked to do it a second time.
The Daily Telegraph claims Liam Fox – who was defence secretary in 2010, under then Prime Minister David Cameron – is a "leading candidate" for the job.
He resigned from the post 12 years ago after it emerged that his best man at his wedding, Adam Werritty, had joined him on 18 foreign trips and handed out business cards suggesting he was his adviser – despite having no official role.
Mr Fox was an ardent supporter of Mr Sunak's campaign to be Conservative leader last summer.
Mr Heappey, a former army major who served in Afghanistan, has been an MP since 2015. He endorsed former Prime Minister Boris Johnson during the 2019 leadership election, and went on to serve as his parliamentary private secretary.
It was Mr Johnson who appointed him as parliamentary under-secretary for the Armed Forces in 2020, before promoting him to minister of state two years later.
Meanwhile Mr Glen, a former management consultant, has held a number of government roles including parliamentary under-secretary for arts, heritage and tourism (2017-18) and city minister (2018-22).
The change to Mr Sunak's top team comes after Mr Wallace said last month that he would leave his post at the next reshuffle of government ministers, and Parliament at the next general election.
Mr Wallace has served continuously as a minister under five prime ministers, having originally been appointed by Mr Cameron as a government whip in 2014.
He went on to be a Northern Ireland minister, security minister and has been defence secretary since July 2019.
Downing Street refused to comment on the reports surrounding Mr Wallace's replacement.
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