Cardiff City FC has three months to produce a business plan for its proposed 30,000-seat stadium.
The new stadium is planned for land near Ninian Park
A meeting of Cardiff council's executive on Thursday imposed a 90-day deadline from 31 December for the club to prove the project is viable.
The club, which last season faced a financial crisis and is also losing income due to low crowds, had asked for six months to satisfy the council.
Cardiff City has said it remains confident the stadium will go ahead.
The council's executive agreed with its economic scrutiny committee who last week said the stadium project was not viable as it stands.
The club asked for another six months to produce new plans, but the council's executive said the Bluebirds should receive 90 days from New Year's Eve to prove the viability of the project.
The club plans a 30,000-seat stadium, which could rise to a 60,000 capacity, on land at Leckwith, near the club's current Ninian Park ground.
Integral to the scheme is securing retail development. American discount store group CostCo earlier this year signed a contract to become a tenant but other stores are needed to join the project.
Scrutiny committee chairman Ralph Cook, said: "As a councillor, I have a duty to the taxpayers of Cardiff... to ensure that the council gets the best value.
Cardiff City want to move from their Ninian Park ground
"We would have considerable community benefits from this stadium proposal and the associated retailing if it went ahead. But we can't wait forever."
Last week, Cardiff City's deputy chairman, Peter Ridsdale, told the BBC news website that he was confident the stadium scheme would go ahead.
The club last season faced £30m debts and sold several players in an effort to reduce wages.
The club is currently having a successful season on the pitch and lies in the play-off positions in the Championship - English football's second tier.
But disappointing crowds mean the club is losing income.
A crowd of 8,724 for Monday's 2-1 win over Ipswich was the Bluebirds' worst home league attendance in four seasons.
Some fans have said they fear low attendances could jeopardise the stadium project.
Tony Jeffries, who has supported Cardiff for more than 40 years, said: "In the last couple of months, doubts have started to creep in and I just hope they don't come true.
"I've always been very positive about it (the stadium), but because of the crowds we are getting, the money people behind it might say 'No, this isn't viable'."
Mr Jeffries believed high ticket prices were to blame for low crowds.
He added: "There's instances where people go on a match day to the Bob Bank (stand) - a father and son is £36 for the two of them, that's disgraceful.
"It should be under £20 for a father and son to sit at a football match at this level."
In a statement on the club's website, Cardiff City said that due to average attendances running 2,000 lower than their break-even point of 13,000, they expected to suffer "a reduction of income of £600,000 over a whole season".
The statement added: "We will continue to do all that we can to tempt our missing supporters back to Ninian Park and hope that our on-field success will bring an increase in support."