Kildare County Council has branded Conor McGregor and his partner Deirdre Devlin's plans to revamp their Straffan home as "inappropriate".
The local authority has asked for further information on the project.
It said given the sensitive location of the River Liffey Valley, the proposed extension, by virtue of its size and scale in relation to the existing home is "inappropriate" and doesn't comply with the county development plan.
It asked for a revised proposal to be submitted.
Last August, Julie Ann Colgan applied for planning permission to demolish the garage at The Paddocks, Castledillon, Straffan as well as a roof canopy, porch and the wing at the side and rear of building. In the planning documents, Deirdre Devlin gave permission to Ms Colgan to make the application on her behalf.
The couple want to build a new extension with a first floor balcony, relocate the tennis court, and install a sunken basement to house a car park, gym and other rooms on the site of the old tennis court.
The plans were drawn up by Tyler Owens Architects.
The council also asked that the applicants submit a visual impact assessment, taking into account adjacent properties and signficant vantage points along the River Liffey and surrounding countryside.
Details on waste water treatment systems were sought.
The applicants now have six months to respond.
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