Carlton Power plans to build a plant in Trafford which would generate enough electricity to power two million homes.
The firm secured an annual £30m government contribution for the next 15 years, but originally had to raise the rest of the cash by September.
Carlton Power now has until 19 December to secure the investment.
The Department of Energy and Climate Change is proposing to shut all coal-fired plants by 2025, and replace them with gas-fired power stations.
The government's capacity market scheme aims to encourage the construction of new power plants and keep existing ones going.
The Trafford power station is the only new major gas-fired power plant to be offered the capacity market contract.
This will be terminated in December if Carlton Power is unable to secure financial backing.
A company which wants to build a government-subsidised £800m gas-fired power station in Greater Manchester has been given more time to secure funding.