THE GAA's transport submissions for the Casement Park stadium project have been deemed "unacceptable" by the Stormont department tasked with deciding whether to grant planning permission.
Roads officials in the Department for Infrastructure (DfI) said "insufficient detail is available on transportation issues" and requested more information.
Transport assessments in four out of five scenarios outlined in the west Belfast plans were also considered "unacceptable".
The issue emerges after a senior official behind Ireland's bid to host the 2023 Rugby World Cup said they were "confident" the stadium would be ready for the tournament.
Casement Park is among several northern venues that would hold matches as part of the cross-border bid.
A delegation including taoiseach Leo Varadkar and former Ireland captain Brian O'Driscoll travelled to London on Monday to make a final presentation to world rugby chiefs.
David Sterling, head of the Northern Ireland Civil Service, also took part in the absence of Stormont ministers.
Work to redevelop Casement was due to begin two years ago, but in 2014 planning approval for the original 38,000-capacity design was overturned in a High Court challenge.
A revised planning application was submitted in February with a reduced spectator capacity of around 34,000.
Ulster GAA hopes to finish construction in 2019, but that depends on the new plans being approved and meeting any further legal challenge.
Residents behind the previous legal action have remained opposed, saying it is "not a significant reduction" in capacity.
Civil servants in DfI will decide on the plans if no new Stormont executive is formed.
In a consultation response released yesterday, DfI's roads team said: "DfI Roads considers the application unacceptable as submitted. Insufficient detail is available on transportation issues."
They said that "should Planning Service be minded to progress the application towards an approval" they would require several "points to be addressed".
They added: "The primary aspect is the fact that the full operation of the stadium has been assessed against the current capacity of the road network relevant to the times each scenario takes place.
"The impact of traffic has not been fully mitigated across all spectator scenarios."
On Monday, Irish Rugby Football Union chief executive Philip Browne was quizzed during Ireland's presentation to the World Cup committee about infrastructure including Casement.
"In terms of Casement Park stadium in Belfast, we are confident that it will be ready in time as it progresses through the stages of its re-development," he said.
The Casement project has been hit by various setbacks over the years, with its cost topping £9.2 million before construction work has even begun.
An overall budget of about £77m has been set aside including £62m of public funds, but it is unclear if the delays will cause the cost to increase.
Ulster GAA has hailed the project as providing "outstanding sporting, community, cultural and economic opportunities".
