The stock slumped 6.94 per cent to Rs 134.80 on BSE. During the day, it dipped 7.83 per cent to Rs 133.50.
At NSE, shares of the company tumbled 6.93 per cent to Rs 134.80.
The company's market valuation fell by Rs 1,863.57 crore to Rs 24,999.43 crore.
On the volume front, 9.96 lakh shares of the company changed hands at BSE and over 82 lakh shares were traded at the NSE during the day.
"The downgrade also reflects Fitch's expectation that capital buffers are unlikely to improve significantly even though the state is likely to inject capital into the bank in the financial year ending 30 March 2016 (FY16), with the bank's large stressed assets stock potentially taking longer to resolve than that of its peers," it said.