Why not Nicolas N'Koulou? Out of contract in the summer, has just turned 26, has played under Bielsa at OM (and shared a great rapport with the guy, by all accounts, which bodes well for his potential adaptation to our style of play), and is well suited for the dual CB/DM role a la Dier, given that he's been played at DM for large portions of his career (and was considered the heir to Rigobert Song at one point).
Being Cameroonian, he might give N'Jie some company too, since Clinton's been noticeably absent in the high-spirited banter our lads get up to most days.
But in all seriousness, if backup for Dier's what we need, we should consider N'Koulou on a free. Wanyama....eh, I can't see it.