The cost of building the athletes village for the 2022 Commonwealth Games in Birmingham is set to rise by £91.8m.
The city council said a "construction cost price inflation" and increased demand for building workers had helped tip the cost over the £496m budget.
Its revised budget says it aims to reduce the extra £91.8m costs by £25m.
Ian Ward, leader of the Labour-run council, said the importance of the project for the 2022 Games and the city "cannot be underestimated".
It follows months of speculation over the cost of the village being built for competitors in Perry Barr.
Robert Alden, leader of the opposition Conservative group, said it "laid bare Birmingham City Council's mismanagement of its own contribution" to the Games.
He said £7m had been removed from the cost by "reducing the number of bed spaces to "97% of that originally required". He also criticised the Labour cabinet for making the report "exempt from call-in" which means it cannot be scrutinised by backbenchers.
Birmingham City Council has pledged to build accommodation for up to 6,500 athletes for the 2022 games, under its host city contract.
After the event, it will be converted into 1,400 homes for sale and rent, including social and affordable housing.
Kathryn Stanczyszyn, Birmingham political reporter
Worries about a black hole when it comes to cash for the athletes village have been on the horizon for a while.
The Labour-run administration says it's simply not its fault - blaming inflation from an "overheating construction market" for the majority of the rise in cost.
Leader Ian Ward has also said previously the government "has failed to help mitigate" the financial risk of this massive capital spend.
But critics say ministers have found quite enough cash already, thank you, for the half a billion pound Perry Barr development - on top of the actual games budget - and that this "monster overspend" is down to mismanagement.
The council says it has already found £25m of this extra bill - and it will find ways to mitigate impact on taxpayers. But some think that'll be impossible.
Mr Ward said it would become "one of the most vibrant, dynamic and well-connected" parts of the city.
"It is a catalyst for many improvements in Perry Barr, which would have been delivered at a much slower pace or not at all if it were not for the investment the Commonwealth Games is levering into Birmingham," he said.
The revised business case goes before the cabinet on 17 March.
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