Bradford & Bingley's (B&B) share price has closed 19% lower as worries persist about its fundraising plans.
Shares fell as much as nine pence to a new low of 33p, with reports that one City broker had rated them worthless.
The Daily Telegraph reported that stockbroker Pali International had cut its target price for the bank to zero.
B&B was hit last week when credit agency Moody's downgraded its debt, prompting Texas Pacific Group (TPG) to scrap plans to invest in the bank.
Although TPG decided to back out of a plan to pay £179m for a 23% stake in B&B, the bank managed to salvage its plans to raise £400m after leading City institutions rallied round to provide the cash.
The latest fall in the share price means that the shares are now well below the 55p rights issue price currently being offered to shareholders.
"This third attempt at a rights issue looks like a dog's breakfast," said David Buik at Cantor Index.
"Though depositors' funds are safe, and in no way can this bank's problems be seen as a replication of Northern Rock, we can only hope that the management of this beleaguered mortgage lender and its advisors have plan B in place," he added.
Shares closed 8 pence lower at 34p on Tuesday.
On Monday, banking analysts at Fox-Pitt, Kelton cut their target price for B&B shares to 43p on the assumption the rights issue was completed at the 55p subscription price and the Bank of England and Financial Services Authority ensured B&B did not "fail".
Fox-Pitt, Kelton said that: "However, we cannot rule out the possibility of an effective failure, with shareholders receiving little or nothing for their shares."
B&B will hold an extraordinary meeting on 17 July to gain approval for its revised fundraising plans.