He is reportedly suffering from high blood pressure.
Siwela’s lawyer, Matshobana Ncube of Abammeli Lawyers for Human Rights on Friday said his client’s condition was deteriorating daily.
He said the 2002 independent presidential candidate was admitted at the hospital on May 20.
“He is not feeling well,” Ncube said. “There is no clear-cut improvement, he is still critically ill.
“High blood pressure is a condition that kills and we are afraid of the worst.”
Siwela together with two other MLF leaders, John Gazi and Charles Thomas, were arrested in March and charged with treason for allegedly distributing the group’s pamphlets calling for a separate Matabeleland state.
Gazi and Thomas were freed on bail last month but Siwela’s freedom was blocked by state prosecutors who claimed he had a pending case.
He appealed at the Supreme Court and Chief Justice Godfrey Chidyausiku early this month postponed a hearing into Siwela’s bail application.
He instructed him to deposit an affidavit assuring the court that he would not commit any offence of a treasonous nature as a precondition before his bail application could be heard.