Plans to build a national stadium at Lansdowne Road are unlikely to get planning permission unless the Irish Rugby Football Union (IRFU) cuts the size of its proposed development, the Office of Public Works (OPW) has indicated.
The IRFU, supported by the Football Association of Ireland (FAI), this month proposed to build a €250 million, 50,000-seater stadium at Lansdowne Road following demolition of the existing stadium.
Reviewing plans for a national stadium at Lansdowne Road or Abbotstown, the OPW said Lansdowne was at "greater risk" of falling to a planning objection than the west Dublin site.
This doubt about planning permission may lead to new delays in the already long-overdue facility.
The OPW's reservations about the scale of any redevelopment at Lansdowne Road could damage the hopes of the Minister for Arts, Sport and Tourism, Mr O'Donoghue, for bringing a package to the Cabinet early in the New Year.
According to the OPW, the Lansdowne Road application would be "unlikely" to be accepted unless seat numbers were kept to 45,000, the number of games limited and "significant restrictions" imposed on concerts.
In a recent letter to the Government, the chairman of the OPW, Mr Sean Benton, said a 45,000-seater stadium would cost between €295 million and €330 million - significantly more than that estimated by the IRFU for its larger proposal.
"While [the 45,000-seater stadium] would satisfy the FAI's requirements, it is unlikely to be acceptable to the IRFU," Mr Benton said following an examination of a number of studies.
A later study by consultants Ove Arup supporting a 50,000-seat stadium was presented to Mr O'Donoghue earlier this month by the IRFU chief executive, Mr Philip Browne.
The bowl-like stadium, modelled on one in Huddersfield, England, would not require the pitch to be moved from its present north/south axis and would be capable of catering for major rugby, soccer and GAA matches.
Describing it as "a vast improvement", Mr Browne said new stands at the Havelock Square and Lansdowne Road ends would be no higher than Lansdowne's existing terraces.
Reviewing earlier plans for a much larger national stadium, the OPW chairman said in the letter seen by The Irish Times: "An examination of the business model shows that projected attendances only exceed 52,000 for five sporting events in a two-year cycle."
Any reduction in the size of the proposals for either Abbotstown or Lansdowne would "ameliorate, to some extent, the planning difficulties likely to be encountered at either site".
"However, in the case of Lansdowne Road, the reduction would have to be of the order of 20,000, at a minimum, before it would have an appreciable impact on the overall mass of the stadium," Mr Benton wrote.
A 65,000-seater stadium could be "comfortably" accommodated at Abbotstown, and built more cheaply there than at Lansdowne, though it has "the perceived drawback" of being an out-of-town location.
However, Mr Benton warned "significant" local objections were inevitable unless decisions were taking to upgrade the M50 motorway and Dublin/Maynooth railway line.
A 45,000/50,000-seater stadium would "meet all of the needs of the FAI and most of the needs of the IRFU" - though it would require Croke Park to be available for the biggest games.
"Whether a 45,000, 55,000 or 65,000-seater stadium is built at Lansdowne or Abbotstown the cost involved will be high, ranging from €295m to €460m," Mr Benton wrote.
"It would seem, therefore, that, irrespective of site selection, the focus of consideration, initially, should be on stadium capacity and on the level of investment available for delivering that capacity."
