Nielsen, who was appointed in August this year, officially designated as the "high-performance red-ball coach", had seen his contract run out; it was up for renewal after Pakistan's tour of Australia, and he had been waiting to hear about a decision on an extension. He told ESPNcricinfo he felt he was "making good progress" with the team and was fully committed to the Test series against South Africa and West Indies, but that the PCB had told him his services were no longer required.

It is understood the PCB did not inform Gillespie ahead of time he would no longer have his assistant coach by his side in South Africa, a decision that has left him extremely unimpressed. That he wasn't consulted beforehand appears to be the most significant catalyst for his irritation, and fits in with a wider pattern of Gillespie's roles and authority being steadily eroded over the last few months.

In October, he was removed from the selection panel for the Test side and said he was now merely a "matchday strategist". There was limited communication between the player and the board since the end of Pakistan's white-ball series in Australia, where he coached the side on an interim basis after Gary Kirsten quit.

Gillespie's anger is understood to partly stem from what he felt was a great rapport Nielsen had developed with the players, a point he had made more than once in public. It is believed both Gillespie and Nielsen consider the fact that Nielsen is not based in Pakistan as the reason his contract hasn't been extended, though, as Nielsen confirmed, he would have been available for the upcoming two tours in their entirety.

While it is understood the PCB has not yet made a decision on any potential replacement for Nielsen, the current administration has sought to replace overseas coaches it appointed earlier in the year with Pakistan-based ones. The PCB has, in the past, attributed not spending enough time in Pakistan as a reason for their dissatisfaction with overseas coaches, most notably in the case of Gary Kirsten, who quit in October. Gillespie, though has always maintained he has met his contractual obligations in that regard.

While it is understood Gillespie has not ruled out the possibility of walking away before the series against South Africa, the terms upon which his stint at the PCB ends remain crucially important in what happens next. If the PCB decide to sack him, they could potentially be on the hook for paying out the vast majority of what remains of his contract, which runs till mid-2026. Should he resign of his own accord, that payout is significantly lower.

Gillespie is scheduled to travel to South Africa from his home in Australia on December 13. Pakistan play the first Test in Centurion on December 26, with the second in Cape Town starting on January 3.

ESPNcricinfo has reached out to the PCB for comment, but has not received a response.