British bank Abbey National does not plan to post details of Santander Central Hispano's agreed bid to its shareholders until next week at the earliest.
The bid's scheme of arrangement, with its additional information on SCH's agreed offer worth £8 billion plus, will not be sent this week, the sources said.
Abbey National and SCH declined to comment.
Sources had said last week that Abbey planned to post the document to shareholders as early as the second half of this week.
Publication of the scheme sets the clock ticking on SCH's offer as it marks the start of a three-week minimum notice period before shareholders can meet to vote on the deal.
Analysts and sources familiar with the situation have said it could help trigger counterbids from UK banks such as HBOS, which may want to sift through the document for new details of the Santander agreement before deciding on their own bids.
HBOS, Britain's largest mortgage lender, said in August it was considering challenging SCH's largely equity-based bid.
Under the scheme of arrangement, counterbidders would have until Abbey's extraordinary general meeting - expected in October - to state their intention to make an offer. The meeting must be at least three weeks after the document is sent.
SCH is using a scheme of arrangement rather than a simple offer document to bid for Abbey, because under a scheme it would win 100 percent ownership of Abbey once 75 percent of Abbey shareholders approved the bid.
Under a regular takeover offer, a bid only needs 50 percent shareholder approval but if less than 90 per cent of shareholders approve it, there is a risk the bidder will not get full control.