The France international kicked off the season with a run of impressive performances but a thigh problem suffered in the September defeat to Chelsea meant that was the last of his six appearances this term.
Diaby has endured long spells on the sidelines through a succession of serious injuries during his Arsenal career, and Wenger has admitted he is unsure of when he will return.
"I cannot give you any fixed date because we are a bit in no man's land on that front," said the Arsenal manager.
"He is working, but we are waiting for him to come back. He is not ready."
Wenger confirmed Olivier Giroud and Laurent Koscielny are likely to return to the squad for Monday's Premier League clash with Reading, while Theo Walcott remains sidelined.
Koscielny, who suffered a groin strain against Everton in November, will most likely take up a position on the bench, while Giroud, who missed Wednesday's shock defeat by Bradford, returns following a knock sustained in the win over West Bromwich Albion.
Walcott hasn't featured since injuring his calf in the defeat against Swansea at the beginning of the month and it remains to be seen when he will return to the Arsenal line-up.
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