Freedom House envoy Damon Wilson said Yulia Tymoshenko was unable to sit or stand and had to lie in bed at Kharkiv's Kachanivska prison during the delegation's entire visit on April 4.
Wilson said receiving proper medical care was the most critical issue for Tymoshenko, who's serving a seven-year sentence on charges of abuse of office.
He expressed concerns Tymoshenko was not receiving adequate medical care from prison doctors.
On April 3, Freedom House officials visited jailed former Interior Minister Yuriy Lutsenko in a Kyiv detention center, where he is serving a four-year sentence for alleged embezzlement as well as abuse of office.
Both Tymoshenko and Lutsenko pleaded not guilty in their trials, saying they were victims of political persecution.
Their convictions have been condemned by the United States and European Union as politically motivated.
The EU has also called for Tymoshenko to receive hospital treatment outside of prison.