A Dutch court has deferred until Thursday a crucial decision on whether banking group ABN Amro, the subject of a bid battle, can sell its US business.
Analysts believe LaSalle's future holds the key to the bid battle
Investor group VEB is trying to block the $21bn (15.4bn euro) sale of LaSalle to Bank of America, arguing this would be illegal without investor approval.
The outcome could be key to deciding which of Barclays or Royal Bank of Scotland (RBS) succeeds in their bids.
Barclays has bid £45bn for ABN while an RBS-led consortium also intends to bid.
The consortium - which includes Belgium's Fortis and Spain's Santander - has said it plans to offer £49.4bn for ABN but has yet to make a formal bid.
If either of the bids is successful, it would create one of the world's largest banks.
The fight has been complicated by ABN's decision to sell US unit LaSalle, a move which Barclays approves of but RBS opposes.
RBS bosses will be following the outcome of the ruling with interest
The RBS-led consortium has said its bid is dependant on the reversal of the LaSalle sale.
Meanwhile, Dutch shareholders association VEB has filed a suit to prevent the LaSalle sale going ahead, claiming it would stop ABN from talking to other potential bidders aside from Barclays.
ABN has argued that Dutch law only requires explicit shareholder backing for the sale of any business accounting for a third of total sales.
Should the Amsterdam District Court decide in favour of VEB, it is likely to delay the sale of LaSalle and potentially derail the Barclays deal.
The decision could, in turn, prompt legal action from Bank of America.
RBS and their partners say their proposed offer for ABN represents better value for shareholders than Barclays' bid, which has been recommended by ABN directors.
ABN shareholders have urged the bank's management to sell to the highest bidder.