To be fair it's a bit of a stitch up by the media, it's a mischievous question - he's hardly going to say "dear God no!" in public when asked about a new contact for Diaby.
Any other manager would've got rid of him 4-5 seasons ago
Our Man Arsene is not a man who can deal with confrontation, so it's easier for him to prevaricate and say "not sure we will deal with it next month" and then say the same thing again the next month.
I think he's hoping Diaby gets fed up waiting and leaves, but that's like hoping that Wesley Snipes would decide to pay his Taxes off his own back