According to a family source, Mitra complained of stomach pain last night following which a doctor was called to attend him at the hotel in the southern part of the city.
The former state transport minister was attended to by the doctor who administered an injection last night after which Mitra's health condition improved, the source said.
"There is nothing to worry, but doctors have prescribed him complete rest. He has also been asked not to talk much and avoid any form of stress," the source said adding doctors were keeping a close watch on the leader.
Mitra was released from Alipore jail yesterday morning and taken to a hotel within the Bhowanipore police station limits as per the condition set by the court for granting him bail. His own residence is within Kalighat police station limits.
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Alipore sessions court granted Mitra bail on Friday on two sureties of Rs 15 lakh each.
He was directed to appear before the court on November 23, surrender his passport to CBI and appear before its investigating officer once every week. He was also directed not to leave Bhowanipore police station jurisdiction area.
Former union minister Matang Sinh is among those arrested in the case, while several TMC functionaries, including Mamata Banerjee's close aide Mukul Roy, have been questioned in connection with it.
The CBI had taken over the investigation to the Saradha chit fund scam in June, 2014 on the order of the Supreme Court.