Middlesbrough boss Gordon Strachan believes Stephen McManus has had a positive impact on centre-back David Wheater since his January move.McManus, 27, and Wheater, 23, have struck up a partnership at the heart of the Boro defence and Strachan sees McManus's presence as a key factor. [LNB]"McManus is not much older than Wheater but he has had so much experience," Strachan told BBC Tees. [LNB]"He loves to be a leader, and I think David is enjoying that." [LNB]McManus is currently on-loan at the Riverside until the end of the season, although Boro would be keen to make the move permanent. [LNB]Boro continue to chase down a play-off place in the Championship, with a four-point gap between the club and Swansea in sixth. [LNB]And their pursuit of the promotion places continues with the trip to West Bromwich Albion whose place in the Premier League is already secured. [LNB][LNB] [LNB][LNB] Strachan is convinced the key to the Baggies' success has been a settled line-up under Tony Mowbray, and then his successor Roberto Di Matteo. [LNB]"They've been together a wee while, the know each other, they've kept that squad together when it's gone up and down," [LNB]"There's a nucleus there and and they've added good players like Graham Dorrans to the team and he's been magnificent this year, and there's good players there in [Chris] Brunt, [Robert] Koren, [Roman] and Bednar. [LNB]"They've got a lot of goals, they can get goals from midfield, which means you don't have to rely on two or three strikers."