Tymoshenko is serving a seven-year prison term after being convicted of abusing her authority when, as prime minister in 2009, she helped broker a gas deal with Russian energy company Gazprom. That deal returned gas supplies to Ukraine but the current government claims it ruined an economy battered by recession.
A Ukrainian court of appeals is to hear the case Thursday in Kiev.
A colleague, however, said the former prime minister likely won't attend because of poor health.
"Yulia Tymoshenko is unlikely to participate in the court hearing because, unfortunately, her health is deteriorating quickly," Oleksandr Turchynov, deputy head of the opposition the All-Ukrainian Union "Fatherland" party was quoted by her Web site as saying.
Ukrainian President Viktor Yanukovych ordered Tymoshenko transferred to a pretrial detention center's "European-standard" medical ward earlier this week.
Doctors during Tymoshenko's most recent checkup were unable to pinpoint the cause of her ailments though her lawyers have said she's unable to get out bed.
Her Western supporters say the charges against her are politically motivated. She lost a bruising 2010 campaign for president to Yanukovych.