The deal is worth $96.8 billion but the consortium are hoping that if they wait until debt prices have normalised then the cost of funding will have reduced.
Speaking to City AM, an un-named source said: "You can understand why the consortium would want to delay. They will probably have to delay. They would have to lock in levels now that would effectively add an extra Â£2-3 billion ($4-6 billion) to their costs."
The bid is financed by RBS, Fortis and Santander, and it emerged that earlier in the week Santander had been forced to use its retail customers' support to finance the move.
The problems in funding follow rival bidders Barclays response to seemingly admit defeat on the deal.
Bob Diamond, president of Barclays, said at the time that if the consortium still wanted to pay the price and could raise the money then they would beat Barclays' bid.
Santander is thought to have raised the cash through a $6.9 billion five-year convertible bond.