Earlier this month, the European Commission ordered Royal Bank of Scotland and Lloyds Banking Group to sell off significant areas of their operations due to the large amount of government aid they have received.
Speaking at an Australia-Israel Chamber of Commerce lunch, Mr Clyne said NAB had a keen eye on what was occurring in the UK's financial sector.
"We're watching it very closely and are very keen to see how it develops," he said.
"We've got one of two routes â either expand or get out."
NAB owns two British-based banks, Clydesdale Bank and Yorkshire Bank, which have come through the financial crisis without the need for state aid.
Last month, NAB reported profit levels for the first nine months of the year of $879 million at its two UK operations.
By Claire Archer