The PM is finishing off his limited rejig of his top team, to replace the Defence Secretary who is stepping down and quitting Parliament.
Senior government sources said ministers are on standby for the imminent announcement.
The Defence Secretary is understood to have handed over a list of his preferred candidates to the PM, who is remaining tight-lipped about his new appointment.
Mr Wallace announced his shock resignation last month – after The Sun revealed he was considering his future.
Mr Wallace will leave the post after seven years in the top job, despite being the most popular Cabinet minister among the grassroots, and once the favourite to become PM.
Names floated around Whitehall to replace him include Treasury minister and Rishi loyalist John Glen, Cabinet Office minister Jeremy Quinn, and Armed Forces minister James Heappey.
But Mr Sunak is expected to save a wider reshuffle of his top team ready for the next election, for after party conference season and the King’s Speech in November.
Home Secretary Suella Braverman is expected to stay in post, despite some Tory MPs cooling on her.
One ex-Minister said: “You have to get rid of Suella. She seems too interested in picking fights than solving problems like small boats.”
Other ministers tipped to be shuffled out of the Cabinet include Environment Secretary Therese Coffey – previously deputy PM under Liz Truss.
No10 last night declined to comment on the timing of the upcoming reshuffle.