Also, I think the Mustafi signing is absolutely critical not just because Mertesacker is injured. Koscielny cannot be relied upon every single time, we really need to get him a good partner. Gabriel could be great, he could be rubbish, he needs more time.
Holding, Chambers, Bielik are the prospects. I am most excited about Bielik to be honest, his passing range is really impressive for a young guy, Wenger wants him to play CB.
Re Mertesacker, I think he has ****ed up many times over the years, and Wenger's problem is too much faith in a player. It is nothing to do with tactics imho, I just think Mertesacker has been a liability because of his lack of pace and Wenger's rep has taken a hit because of that faith. You look at our defence and he is a clear weak link. If you get a competent CB next to Koscielny we look really good in defense. Of course, that is supposing our first team defense keeps fit and we don't need to play Gabriel for big games away at Stamford Bridge and Old Trafford.