There is a famous story of how several years ago during a lunch, Wenger revealed his most prized asset. It wasn't' Fabregas, or RVP, or Nasri or Wilshere but rather Abou Diaby. It's fair to say were Wenger not the Arsenal manager, Diaby's career at the top of the game would have ended by now.
He has had consecutive long-term injuries and is rarely fit, and when he is, doesn't manage to demonstrate his potential. He did against Liverpool earlier this season in what was arguably one of the best individual performances you'll see of a player for a long while. But he has only played just nine league games in two seasons.
Wenger had this to say about him recently:
The situation for Diaby is so frustrating and for us as well we started the season well with him in the team and since he has been out we have felt it. I can tell you he has been everywhere in the world to be assessed. There is an explanation. He is quick, strong, has good stamina, good resistance to repeat, but his muscle strength is not good enough to deal with that. Sometimes little fibres go in his muscles, this is basically his problem. When you play every three days, you cannot rebuild your strength as you need to recover. When you don't rebuild your strength, through the games you burn your fibres a bit and become weaker and weaker, so that means he gets injured. The second reason for his problems of course is his ankle. Since he was slaughtered at Sunderland, his mobility in his ankle has been affected.
His career is finished in my honest opinion.