Mitra had complained of chest pain and respiratory distress on December 19 following which he was admitted to the state-run SSKM Hospital from Alipore Central Jail.
"Nothing significant was found in the medical tests. The medical board felt that there is no need to keep him in the hospital any more. Once the formalities are completed, the jail authorities will take him back," SSKM director Pradip Mitra told reporters.
Mitra was arrested on December 12 by CBI and has been remanded to judicial custody till January 2.