ESPNcricinfo understands the decision could be announced as early as Monday. It is the day Pakistan play their final white-ball game on their ongoing tour of Australia - the third T20I of a series Australia have already wrapped up 2-0. As things stand, it would be Gillespie's final engagement of a brief, tumultuous time as head coach.

It is understood Aaqib was not the PCB's first choice, with the board initially sounding out Gillespie to take over as all-format coach until the end of the Champions Trophy next March. However, he was asked to take on the additional white-ball responsibility without a change in his current contract: in effect, to take on two additional formats without being paid more for the increased scope of his role. Gillespie turned that offer down, prompting the PCB to decide they did not wish to have him in charge of the red-ball side, and beginning the search for an all-format coach.

A PCB official, though, attributes the decision to replace Gillespie down to him not spending enough time in Pakistan. It is something the PCB had privately used to explain the resignation of Gary Kirsten, the most recent white-ball coach before until he quit last month. ESPNcricinfo understands Gillespie's view is that he has spent every day his contract demanded he be in Pakistan within the country, in addition to which he also did the Shaheens tour of Darwin without pay as a gesture of goodwill.

How much time Gillespie needs to spend in Pakistan is a moot point at the moment. They have no cricket at home for the next two months in any format and go directly from Australia to Zimbabwe, after which they play an all-format series in South Africa. Their next home engagement is a two-Test series against the West Indies at the end of January, and their only white-ball games before the Champions Trophy come in a short tri-series against South Africa and New Zealand in February.

After the PCB began looking for a coach, they initially considered the possibility of either elevating Azhar Mahmood, or appointing Saqlain Mushtaq, who served as coach in from 2021-22. Neither, though, appeared to draw enough support from within the PCB's advisory circle, which led to Aaqib being offered the position. It is understood he will be asked to take on the role until the end of the Champions Trophy, following which the PCB will reevaluate.

Gillespie's time - should it come to an end, as expected - has been eventful. It began ignominiously when Pakistan slumped to a home 2-0 defeat against Bangladesh, but things turned around with a come-from-behind 2-1 triumph against England - Pakistan's first Test home series win in nearly four years. With Kirsten resigning soon after, he was appointed interim white-ball coach for the tour of Australia, and oversaw Pakistan's first series triumph in the country in 22 years, turning around another opening-game defeat by romping to two crushing wins in the ODI series. The T20I series that followed was rain-curtailed, but Australia wrapped it up with a game to go.

A decision to part ways with Gillespie would also draw a close to a remarkable year in Pakistan's pursuit for coaching staff. Last November, Mickey Arthur, then team director, was told by then PCB chairman Zaka Ashraf he would not be going with the team for the Test series in Australia - Mohammad Hafeez performed that role instead. Arthur and Grant Bradburn, then head coach, left soon after. Mohsin Naqvi assumed the PCB chair weeks later, beginning the hunt for what he called "the best possible coaches", ultimately appointing Gillespie and Kirsten.

At the time, he said "their stellar track records preceded them" and that they would be given independence to work with their respective sides. Six months later, Kirsten had left, without coaching Pakistan in a single ODI - the format that he won the 2011 World Cup with India in. Gillespie, it appears, is set to follow him out of the door imminently.

For Aaqib, meanwhile, the speed of his ascent has been supersonic. Until a few weeks ago, he was Lahore Qalandars' long-term coach and director of cricket operations, where he had a mixed record; he led the side to consecutive PSL titles, but also saw several bottom-placed finishes, including earlier this season.

When appointed a member of the selection committee, he was viewed by the PCB's top brass as the mastermind behind the implementation of spin-friendly wickets against England to turn that series. He quit his role at the Qalandars to focus on the PCB, where he was initially viewed as the favourite to be appointed director at the National Cricket Academy.

He served a stint as Sri Lanka's bowling coach earlier this year, but now begins his highest profile challenge. Pakistan have a choc-a-bloc cricket season until the Champions Trophy. Six white-ball internationals against Zimbabwe will be followed by as many in South Africa, with two Test matches to come after. Pakistan then play two Tests against West Indies at home and a tri series featuring South Africa and New Zealand before the Champions Trophy, which is set to begin on February 19.