A preliminary hearing in Aleksanyan's case, meanwhile, was cut short Wednesday after the suspect began feeling unwell, Aleksanyan's lawyer said.
In an appeal to Prosecutor General Yury Chaika, Khodorkovsky said he had no choice but to go on a hunger strike to protest the authorities' treatment of Aleksanyan.
"I hope that the department you head will make the decision to guarantee Aleksanyan life and medical assistance," Khodorkovsky wrote in a letter that was posted on his web site, Khodorkovsky.ru.
One of Khodorkovsky's lawyers, Robert Amsterdam, said the hunger strike was understandable.
"Everyone has been totally shocked by this case," Amsterdam said by telephone from Canada. "Mr. Chaika and the executive power need to understand their personal liability in this case. They are giving orders in a system so that is so corrupt that officials can threaten suspects with murder to elicit false testimony."
Aleksanyan, who is facing embezzlement and tax evasion charges, claims he has been deliberately denied medical treatment for AIDS while in detention as punishment for refusing to testify against his former bosses, Khodorkovsky and Platon Lebedev.
Khodorkovsky and Lebedev are each serving out eight-year prison terms after being convicted of fraud and tax evasion in 2005.
The Federal Prison Service claims that Aleksanyan has merely refused treatment.
The Strasbourg-based European Court of Human Rights has issued three requests for Aleksanyan, 36, to be transferred to a special hospital -- requests that have been refused by Russian courts.
Russia is a signatory to the European Convention on Human Rights.
At Wednesday's hearing at the Simonovsky District Court, doctors were called in to examine Aleksanyan after he "suddenly felt unwell," his lawyer, Yelena Lvova, said.
"His temperature rose to 39 degrees, and doctors said he was in no condition to continue the hearing," Lvova said.
The hearing was to continue Thursday, though Lvova said she would "try to postpone the trial" until her client is feeling better.
The judge on Wednesday was to set a trial date and rule whether Aleksanyan would remain in custody, a Moscow City Court spokeswoman said.
Human rights ombudsman Vladimir Lukin sent a letter to Chaika on Wednesday requesting that the prosecutor general "take measures" to secure the necessary treatment for Aleksanyan, Lukin's assistant said.
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