Tymoshenko declared a hunger strike in late April after she claimed she was abused by prison authorities. She's been refusing medical treatment by Ukrainian authorities.
Eugenia Tymoshenko, the former prime minister's daughter, said the opposition leader agreed to undergo treatment if a German doctor was admitted to the treatment process.
"Any interference by people Yulia Tymoshenko doesn't trust, who aren't authorized to make any medical decisions regarding her health, is unacceptable," Tymoshenko's attorney, Serhiy Vlasenko, was quoted as saying on her Web site.
Tymoshenko reportedly ended her hunger strike Tuesday. She is allegedly suffering from chronic back pain and is largely confined to her bed.
The leader of the country's Orange Revolution is serving a seven-year prison sentence on charges she abused her authority when she helped broker a natural gas deal with Russia's Gazprom when she was prime minister in 2009.
Her supporters claim the charges against her are politically motivated. She lost a bitterly contested race for president in 2010 to Viktor Yanukovych.