The former president was put back in a solitary cell at the Seoul Detention Center in July, as prosecutors investigating his short-lived declaration of martial law in December sought additional charges against him.
Yoon is already on trial for insurrection, a charge which is punishable by death or life imprisonment.
He also faces a string of other investigations led by special prosecutors, including one into scandals surrounding his wife, former first lady Kim Keon Hee, where the couple allegedly exerted inappropriate influence over elections.
Yoon has denied any wrongdoing, and his lawyers have accused prosecutors of conducting a politically motivated witch hunt.
The former president has repeatedly rejected requests by prosecutors to appear for questioning, citing health issues.
His lawyers said on Thursday that he was unwell due to pre-existing conditions, including a condition that meant there was a risk of him losing his eyesight.
In a reference to Yoon’s position as a former top prosecutor, Oh, the spokesperson for the special prosecution, said the case was being closely scrutinised by the public.
“The suspect has consistently highlighted the importance of laws, principles, fairness and common sense, and through this case, people are watching if the law applies equally to everyone,” Oh said.
Separately, investigators requested that Yoon’s wife Kim, who has also denied any wrongdoing, attend questioning on Aug 6. Kim’s lawyers have said she would cooperate with the investigation.
Source: CNA
