I honestly think Diame has the potential to be a really good player; someone in the mould of Viera or Yaya Toure. His control of the ball and dribbling look really promising (especially for such a large guy) and demonstrates he has a lot of athleticism and power, both to win the ball and keep it. His passing stats are good too; keeping the ball and creating chances for other to capitalise.
His major problem is his work rate; he doesn't match that of the two aforementioned players, and this has to be because of his heart condition. I don't think its worth the risk. I'd rather someone like Clasie, M'Vila, Sissoko, Matuidi etc.