Scotland's largest council is warning that cuts in spending will be "harder, faster and deeper" than it had originally expected.
Glasgow City Council said it would have to find £40m more in savings next year than it had planned for.
This is likely to lead to bigger cuts in services.
The authority now expects to have to save a total of £115m between 2011 and 2013. It had hoped to delay some savings for longer.
Council officials will now have to find ways of achieving the cuts and balancing its books. The authority is already well on the way to cutting 2,800 jobs over the next three years through retirements and voluntary redundancies.
The budget forecasts are contained in a document circulated to councillors.
Councils across Scotland will not know for sure how much money they will have next year until late in the year. Around 80% of their funding comes from the Scottish Government.
Glasgow City Council is predicting that it will receive nearly £38m less from the government next year. While it expects its main grant to fall by £45m it anticipates getting nearly £8m more so that the council tax can be frozen again.
Finding more ways to save money quickly could prove difficult for the council which has already made significant cuts.
The council is already trying to cut 2,800 jobs over the next three years - many other councils have still to say how many jobs they expect to go. Pay is the single biggest cost which councils can control.
One option may be to try to persuade those who have expressed an interest in voluntary redundancy or retirement to leave more quickly.
The local authority umbrella organisation Cosla is currently proposing that most council workers should have their pay frozen next year although many may still receive incremental rises.
But most of Glasgow's savings will probably have to come through cuts in services and spending. One option will be to look at the running costs of the new Transport Museum which is due to open next year.
In this year's budget, Glasgow City Council reduced the opening hours of some smaller museums and closed some libraries and community halls.
Although councils have a number of statutory obligations, they have a degree of flexibility in how they actually meet them. Some spending is entirely at their discretion.
Councillor Gordon Matheson, the leader of Glasgow City Council said: "The scale of the challenge faced by Scotland's councils in the coming years is staggering. However, Glasgow is not afraid to take difficult decisions and we've started that process already."
Glasgow City Council has long argued that it does not receive its fair share of government money - a charge strongly denied by the government.
Councillor Matheson added: "It is vital that the Scottish government treats local authorities equally and fairly.
"The Scottish government has a terrible record of giving Glasgow a smaller and smaller share of any increases in resources and they must not force the people of Glasgow to take more of the pain when the cuts come.
"Glasgow and Edinburgh are Scotland's economic powerhouses and cutting the cities' throats will not help us out of the troubles we face."
The leader of the council's SNP group, Councillor James Dornan, said: "These are dark days for the public sector in Scotland, thanks to the financial catastrophe wreaked by the last Labour government in Westminster.
"The SNP group will continue to support any sensible suggestions on how to mitigate the effects of this economic downturn."
A Scottish Government spokesman said: "Glasgow receives more money than any other mainland local authority in Scotland - over 25% more than the Scottish average in per capita terms.
"Throughout the current spending review period councils have received an increasing share of the resources available to Scotland - despite our budget for this year being cut by Westminster.
"It is clear we face an increasingly challenging financial climate, but the local government settlement and Scottish Budget for next year can only be agreed once the outcome of the next UK Comprehensive Spending Review is known."
Council officials will now look at options for balancing next year's budget. The final spending decisions are likely to be taken early next year.