Speaking in Paris a few hours before France was to face Ukraine in a Euro 2012 football match, Yevgenia Tymoshenko said her 51-year-old mother's health was not improving after she was treated for a bad back, claimed to have been beaten by guards and undertook a hunger strike.
"I call for pressure to continue on the Ukrainian government," she told AFP as she was hosted by a local mayor's office, saying she had seen her mother the week before in her prison in Kharkiv.
"She is under constant surveillance, under psychological pressure. She still isn't walking. She can't even go as far as the window," Yevgenia Tymoshenko, 32, said.
"They won't even let her use the phone. God knows what could happen to her," she added said.
"Today is a symbolic day. Ukraine is playing against France. I want to thank all those here who support my mother."
Tymoshenko, a driving force of Ukraine's 2004 pro-Western "Orange Revolution", served as prime minister in 2005 and again from 2007 to 2010, when she lost a presidential race to current leader Viktor Yanukovych.
She is serving a seven-year sentence for abuse of power and faces fresh charges that could extend her sentence to 2023.
Her jailing prompted howls of international criticism and the Tymoshenko affair has deeply strained ties between Kiev and the West, which has called for her release.
Her daughter has campaigned in Europe for her release and met officials in Germany last week.