A LAST-MINUTE challenge to the re-development of Casement Park is expected to further delay the project.
A residents' group has filed a legal challenge against the 34,578-seat project, which was granted planning permission by Infrastructure Minister Nichola Mallon in July.
Legal papers for a judicial review of the minister's decision were filed on behalf of Mooreland and Owenvarragh Residents' Association (Mora) on Tuesday.
The GAA had wanted to start building work on the west Belfast stadium next year, following a decade of delays.
However, money for the project is not yet in place.
First minister Paul Givan has previously suggested the cost of the project could rise to more than £140m - almost twice the original budget of £77.5m.
The previous Executive committed £62.5 million to the project, along with £15 million put forward by the GAA.
The association is due to submit a draft business case to the Department for Communities before Christmas.
In a letter distributed to residents, Mora said: "Our legal advisors have identified various grounds on which to challenge the legality of the decision".
Mora described the proposed stadium as "over-sized".
"We acknowledge that the prospects of success are uncertain, as they are in any court setting," the letter read.
"Nonetheless, we believe that we have good grounds for challenging the decision and achieving a positive outcome."
Mora is now waiting to hear if a judge will grant leave for a judicial review. If a review is granted, the project could be delayed by up to six months and may have to be substantially amended.
An earlier court challenge by Mora in 2014 against previous Casement plans lasted around eight months and included around 13 days of hearings.
However, it is understood a potential judicial review in this case would be unlikely to last as long.
Before the legal action was filed, Stephen McGeehan from Ulster GAA told The Irish News that the association was "moving on with our plans to hopefully get started on site next year".
“The overall plan is that we will hopefully start construction in the first half of next year," he said.
The project is a commitment in the 2020 New Decade, New Approach agreement and its construction would complete the 'Regional Stadia Programme', following the redevelopment of Kingspan and Windsor Park.
The GAA said yesterday it is "very disappointed" by the legal action.
In a joint statement, Brian McAvoy, Chief Executive of Ulster GAA, and Tom Daly, Chair Casement Park Project Board, said there was wider support in the west Belfast community for the project.
"The response to the legal proceedings is a matter for the Department for Infrastructure," they said.
"However, as a potential notice party our own legal team are reviewing the submissions made to the court.
"Ulster GAA followed and fully participated in a comprehensive and robust planning process, which lasted for four and a half years, addressing all issues raised by the Department for Infrastructure and all statutory consultees.
"We remain heartened by the vibrant and vast support that there is for the project locally and throughout Belfast, Antrim and Ulster and we would like to thank Gaels and the wider community for their support and patience."
A spokesman for the Department for Infrastructure confirmed legal proceedings had begun.
"The department has received leave papers on behalf of Mooreland and Owenvarragh Residents Association in respect of the decision to grant planning permission for Casement Park," he said.
"Judicial review proceedings are ongoing."
