The lender said it had received "a number of non-binding proposals", and it had selected "several parties" with which to continue talks.
The bank, in which the Co-operative Group still has a small stake, was rescued from the brink of collapse by a group of hedge funds in 2013.
Last month, it reported its fifth annual loss in a row.
On Thursday, the Co-op Group declared the bank worthless, cutting the value of its stake in the lender to zero.
The write-down of its stake in the bank pushed the Co-op Group into a pre-tax loss of Â£132m for 2016.
In its latest statement, the Co-op Bank said that, in addition to talks with suitors, it was also in discussions with existing and other potential new investors to raise capital.
It added that it continued to discuss both the sale process and capital raising process with the Prudential Regulation Authority (PRA), "which has welcomed the actions being taken".
The Co-op Bank put itself up for sale in February after it was unable to reach a strong enough footing to satisfy regulatory requirements.
It blamed low interest rates and the higher-than-expected cost of its turnaround plan for its failure to meet the PRA's rules.
The Co-op Bank says it has received a number of takeover approaches from potential bidders.