I don't know if it's been mentioned, but Djourou did actually have an injury, apparently.

Not to kick WUMger's cadaver further, but recent breakthroughs (Wilshere, Szczesny, Oxtail, Coquelin, perhaps Yennaris) have come through blunder and injuries rather than his faith in them. They've all proved to be successes so far (even those with limited play), so his seniority intransigence becomes even more baffling.