West Brom are paying £8million for Manchester United defender Jonny Evans – and will now sell Joleon Lescott to rivals Aston Villa.
Albion boss Tony Pulis has been trying to lower the average age of his central defence this summer.
Stoppers Lescott, Gareth McAuley and Jonas Olsson are all over 32 years old.
Albion have already signed James Chester, 26, with Evans, 27, having a medical with the Baggies on Friday night.
Evans is yet to play for United this season and won’t be eligible for Albion’s game on Saturday at Stoke.