Since news of that the two banks are in exclusive negotiations about a merger, ABN Amro's stock has shown an increase of 25 per cent.
Commenting on developments to Bloomberg, Christopher of Bear Sterns, said: "We believe that a deal at $45 per share would be a stretch for Barclays [which] will have to put some clever structures in place."
Mr Wheeler added that he thought Barclays will need to offload assets to finance the deal, noting that it may sell the American wing of the Dutch bank's business to Royal Bank of Scotland.
Should the Barclays and ABN Amro merger be approved it is to set to create a bank with a market capitalisation of $80 billion.
However, speculation has been rife that RBS and Spanish bank Santander are set to launch a rival bid.