"The scientist is under microscopic scrutiny," an official close to the investigation told AFP on condition of anonymity.
"We are still assessing the extent of his involvement in the proliferation of nuclear technology. Hopefully, it will be known by the end of this week."
Four other scientists and three security officials associated with Pakistan's key uranium enrichment facility, Khan Research Laboratories (KRL), are under investigation following allegations raised by the International Atomic Energy Agency (IAEA) in November.
They include close aides of Khan, revered as a national hero for providing the key uranium centrifuge designs that enabled Pakistan to develop a nuclear bomb.
At least two individuals were "most likely to be charged with selling nuclear secrets for personal gains very soon", the official said.
"Investigators are trying to establish whether these persons acted under the patronage of Dr. A.Q.Khan due to their close linkage with him."
The nuclear information leaks took place between 1986 and 1993, the official said. The period was within Khans lengthy stay at the helm of Pakistan's nuclear program as chairman of the KRL, named in his honour.
Nuclear technology was clandestinely transferred from Pakistan to the world black market in collusion with operatives from Europe, the United Arab Emirates and Asia.
"There are individuals from Pakistan, Germany, Holland, South Africa and the UAE" who had been named by Iran in its reports to the IAEA, the official said.
Speculation has mounted over the past week that Khans movement has been restricted, and a leading Pakistani newspaper Wednesday said his bank accounts had been frozen.
Officials denied freezing his accounts, but said he had been advised to stay at home.
"There is no such move as banning bank accounts before any formal charges against any individual," the official said.
"He has been politely told to stay indoors, though no official order has been issued," a security officer said.
Pakistan's nuclear program, begun in the 1970s, was covert until May 1998 when it conducted a series of nuclear tests in reaction to rival Indias atomic detonations.
Khan was placed in charge of Pakistan's uranium enrichment after returning home in 1976 from the Netherlands, where he worked for an Anglo-Dutch-German nuclear research consortium.
In March 2001, President Pervez Musharraf removed him from the post and made him special advisor on strategic and KRL affairs.