Yulia Tymoshenko was being treated for back problems after being jailed in 2011 for abuse of office.
Her supporters regard that conviction as politically motivated.
Last year Yulia Tymoshenko claimed to be too ill to attend court proceedings relating to a separate charge of misappropriation of public funds.
The Ukrainian authorities are also investigating allegations against her of tax evasion and involvement in murder.
Yulia Tymoshenko’s conviction for abuse of office relates to a gas deal she signed with Russia as prime minister in 2009, which critics said paid Russia too high a price.
Her supporters say the former prime minister was jailed to prevent her being a political threat to Viktor Yanukovych, the current president.
Yulia Tymoshenko remains a popular politician despite her imprisonment, after coming second to Viktor Yanukovych in the 2010 presidential election.
She was a face of Ukraine’s pro-democracy Orange Revolution alongside Viktor Yanukovych’s long-time rival Viktor Yushchenko.
Correspondents say the health ministry’s announcement will make it difficult for Yulia Tymoshenko to avoid appearing in court.
Previously Yulia Tymoshenko has boycotted trial proceedings against her, and has also staged hunger strikes in protest at conditions in prison and alleged election fraud.
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