On Wednesday, the Health Professions Council of South Africa (HPCSA) tribunal, chaired by Professor Jannie Hugo, adjourned until July 15 to 19, when Knobel is expected to resume giving evidence.
The 75-year-old underwent open-heart surgery early last year.
The HPCSA's professional conduct committee ruled on Wednesday that Knobel's health should be assessed in four weeks to determine whether he would be able to take the witness stand.
Basson is accused of acting unethically by being involved in the large-scale production of mandrax, cocaine, and tear-gas, of "weaponising" teargas, and supplying it to Angola's Unita leader Jonas Savimbi.
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He is also accused of acting unethically by providing disorientating substances for cross-border kidnappings and by making cyanide capsules available for distribution to operatives for use in committing suicide.
United States medical ethics expert Professor Steven Miles previously testified Basson violated the laws of humanity and various World Medical Association declarations and regulations.
However, Knobel, who is Basson's former boss, argued that the Cape Town-based cardiologist was a soldier and not a doctor when he headed the apartheid-era chemical and biological warfare programme.
Knobel disagreed with Miles's view that once someone was a doctor they remained a doctor, and that Basson had made use of his medical knowledge and skills when he headed the programme.
Basson was head of the apartheid government's covert chemical and biological warfare programme, known as Project Coast, from 1981 to 1993.
He has argued that Knobel was in charge of the programme and that he carried out orders as a soldier.
This week Basson called a renowned toxicologist to testify on his behalf at the hearing in Pretoria.
Stellenbosch University's Dr Gert Jacobus Muller gave evidence on toxic chemicals and poisons, including those used in warfare. – Sapa