MPS (BMPS.MI) had scheduled a board meeting on Tuesday to set the terms of an up to 2.5 billion euros ($2.4 billion) share issue, the Tuscan bank's seventh in 14 years after an 8.2 billion euro bailout in 2017.
Rocky markets and the size of the cash call, equivalent to more than 10 times MPS' current market value, have complicated talks over the share sale.
The banks have long seen it as too risky to bring to the market without a pre-committed core of investors.
The new shares will value MPS above healthier peers, exposing underwriters to likely losses on any shares left on their books, bankers and analysts say.
On Tuesday, a source with knowledge of the matter told Reuters that MPS had secured some 30 million euros ($29 million) from local not-for-profit banking foundations in its home region.