Speaking to Reuters, an unnamed source close to the Treasury, said: "Goldman Sachs are advising HMT on some of the mechanics of the guarantee, should it be required."
All deposits in Northern Rock are thought to be safe, after the Chancellor, Alistair Darling pledged all savings would be guaranteed in full.
The bank has been hit hard by the credit crisis and has seen customers queuing outside its branches to withdraw their money.
Goldman Sachs is also thought to be advising the government over future options for Northern Rock which could include a sale or potentially a break up, despite the lack of interest from buyers or hedge funds.
The Treasury told the Times: "We donât disclose advice provided by external advisers."