The leading opposition figure went on a hunger strike after accusing prison guards of beating her as they tried to move her to a hospital for treatment for a back injury.
The news comes as Ukrainian President Victor Yanukovych called off a summit of European leaders after several nations threatened to boycott the meeting over the treatment of Tymoshenko.
The summit, which was due to start in Yalta on Thursday, was cancelled after the presidents of Germany, Romania, Poland and the Czech Republic all agreed to stay away.
The outspoken opposition leader is serving a seven-year jail term after being convicted of abusing her power while serving as the country's prime minister in 2009.
She is also facing a separate trial for embezzlement and tax evasion, and, if found guilty, could see her prison sentence extended by a further 12 years.
Tymoshenko denies the charges, saying they are part of a smear campaign to silence the Ukrainian opposition movement.
German doctors treating Tymoshenko in her prison in the eastern city of Kharkiv have diagnosed her with a slipped disc.
Ukrainian authorities have denied the doctor's requests to have her flown to Germany for treatment, and instead tried to move her to a nearby prison.
It was then that she is alleged to have been punched in the stomach and abused by guards as they transported her for treatment of the spinal condition.
Tymoshenko refused the treatment; fearing doctors would poison her, according to Reuters.