Aston Villa are wrapping up the £9 million signing of West Brom defender Curtis Davies today.
And it will take O'Neill's spending to £14m on central defenders in 48 hours following the signing of Zat Knight from Fulham.
Villa have targeted the England Under-21 star all summer but the Baggies have been holding out for top dollar.
Davies, who cost £3m from Luton two years ago, told boss Tony Mowbray in May that he wanted Premier League football.
But Albion chairman Jeremy Peace insisted his skipper would not be sold on the cheap - and used the fact Spurs were also interested to up the price.