Credit Suisse has been warned it will not be guaranteed the mandate to advise Santander on a possible flotation of its UK business.
Santander is considering a partial stock market listing as a way of raising cash. The bank has already made a similar move with its Brazilian operations, which was widely seen as a success.
A flotation of Santander's UK operation - which includes Abbey, Alliance & Leicester and parts of Bradford & Bingley - is likely to see a scramble among investment banks for the work.
The division could be worth anything from £15bn to £25bn, and would provide substantial fees for the leading banking advisors, which have begun moves to try to curry favour with the Spanish group.
However, a float of the UK division is not likely until next year. Santander is the only bidder for 318 Royal Bank of Scotland branches, and will want to integrate them into its operations before going to the market.
Credit Suisse has been advising on the RBS deal, and a success would be a major feather in its cap after criticism over its role in Prudential's failed attempt to buy AIA.
However, Citigroup is also understood to be working itself into a position to challenge for the role of lead advisor.
"They are all taking this very seriously indeed," said one banking source. "It could be a fee bonanza, and they are desperate for the work.