The source, who declined to be named, said Bo may now be tried in secret and the case was likely to be delayed until at least April.
Reuters reported it had confirmed rumours that Bo, 63, was refusing to cooperate with investigators and had staged at least two hunger strikes.
"He was force fed," a source told the news agency. "He was not tortured but fell ill and was taken to a hospital in Beijing for treatment."
A second source confirmed rumours of Bo's hunger strike and said he had also refused to shave in protest. "His beard is long, chest-length," the source claimed.
"He refused to cooperate. He wouldn't answer questions and slammed his fist on a table and told them they were not qualified to question him and to go away."
A source close to Bo's family said his "strength of character" meant it was unlikely that he would follow the example set by his wife Gu Kailai and his former police chief Wang Lijun, by meekly confessing his sins.
"He will not stand up in court and say what they want him to," the source said.
"I would not be surprised if that is why his trial has been delayed."
Bo was the powerful party chief of Chongqing and a man tipped to rise to the top. He was thought to have his sights set on a position on China's elite Politburo Standing Committee.
But he became embroiled in the murder of the British businessman Neil Heywood in November, 2011.
He was stripped of his position, expelled from the Communist Party and, in August last year, his wife, Gu Kailai, was convicted of poisoning Heywood, 41.
Since vanishing from the public eye last March, Bo's whereabouts have been a closely guarded secret.
When his day in court arrives, he is expected to face charges of corruption and a possible role in covering up Heywood's murder. But the details of his trial remain a closely guarded secret.
A recent report in Boxun, a US-based gossip website, claimed that Beijing feared Bo might seek to air "incriminating information" about other leaders at a public trial.