The France international midfielder had hoped for a breakthrough season after impressing in the Gunners' opening games of the campaign and earned an international call-up, but a thigh injury has scuppered his progress once again.
The 26-year-old has only managed to play in nine Premier League games over the last two seasons and Wenger admitted that Diaby's body is struggling to cope with the demands of the Premier League.
"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," he told ESPN.co.uk
"He balances our team as he has stature and presence physically when he is there, but clearly his injury problems are a concern.
"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."
Wenger also traced Diaby's fitness problems back to a 'slaughtering' tackle made on him by Sunderland's Dan Smith in 2006.
"The second reason for his problems of course is his ankle," he added
"Since he was slaughtered at Sunderland, his mobility in his ankle has been affected."