In her book "Newgrange and the Bend of the Boyne" (Cork University Press) Geraldine Stout has this marked on both of the overview maps of Brugh na Bóinne, and yet there is no mention of it in the index and I haven't come across it in the text, so far. I did see it mentioned somewhere else but can't remember where. Having bought Geraldine's book I decided to see if I could find anything.
I approached from the eastern end of the complex and just where the bend of the road turns sharp right on the long approach up to Dowth there's a small wall. Over this and about 100 metres further west are 2 bowl-like arenas, like hollowed out inverted mounds. Was this where the stone circle once stood? The one further west seems like the most probable. It has 2 large fallen stones that may have come from the circle. One, the northern of the 2, is huge and has definitely been worked/shaped, though, from what I remember, the stones were blasted when the circle was destroyed. The other lies to the south and is thinner and smaller, about 2 metres long.
I've had limited experience of stone circles so I don't know if I've found the precise location. The bowl like depression is about 10 metres deep on its southern side. The floor opens out to the north and drops off until it reaches the modern road about 8 metres below.
Arch. Inventory of Co. Meath says: Possible stone circle (site) Destroyed by quarrying in the eighteenth and nineteenth centuries, the surviving records indicate a circle of large stones set on end some 21 feet in diam. (Studia Hibernica 7, 142-5)