Mr MacAskill said on Wednesday he had informed families and other interested parties that he had reached his decision on the applications for compassionate release and a prisoner transfer.
He will announce his decision at 1300 BST at the Scottish Government's ministerial headquarters in Edinburgh.
A spokesman for the administration insisted the decision had been reached "on the basis of clear evidence and on no other factors".
BBC correspondent Peter Hunt said Megrahi was described as having only months left to live.
"Given this prognosis, it's thought that the perpetrator of Britain's biggest terrorist atrocity - who two days ago abandoned his appeal against his sentence - has now spent his last night in a Scottish jail.
"It's expected he will be allowed to return home to die," he added.
Hillary Clinton: ''We think it is very much against the wishes of the family members''
It is thought preparations for Mr Megrahi's possible release were being made in time for him to be home with his family in Libya by Ramadan, which starts on Friday.
Chancellor Alistair Darling, standing in for the prime minister while Gordon Brown is on holiday, said it was a decision for the Scottish Government.
On Tuesday, judges at the High Court in Edinburgh who accepted Megrahi's application to drop his appeal were told the Libyan's health had recently worsened very considerably.
Megrahi has recently been serving his sentence at HMP Greenock, in the west of Scotland, after being convicted of the bombing under Scots law at a specially convened court in the Netherlands in 2001.
LOCATIONS WHICH SHAPED MEGRAHI'S TRIAL
1. Tripoli, capital of Libya. Megrahi was born here on 1 April 1952, and worked - according to the FBI - for Libyan intelligence services.
2. Malta. Megrahi's day job, as security chief for Libyan Arab Airlines, took him to their office on the island. From there he would travel to Zurich. The bomb began its journey here in December 1988.
3. Zurich, Switzerland. The bomb's timing device was made and purchased here.
4. Frankfurt, Germany. On arrival, a suitcase later found to have contained the bomb was transferred from an Air Malta jet to a flight bound for London Heathrow.
5. London's Heathrow Airport. Pan Am flight PA 103 took off from Heathrow at 1825 GMT on Wednesday, 21 December 1988.
6. Lockerbie, Scotland. The bomb on Flight PA 103 exploded above the Scottish village at 1902 GMT.
7. Camp Zeist, Netherlands. Here, in a landmark trial, Scottish judges convicted Megrahi in 2001.
8. HMP Barlinnie. Megrahi served the first part of his sentence in this Scottish prison.
9. HMP Greenock. Megrahi was transferred from Barlinnie to Greenock in 2005.
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.