See I think maybe he sees Song as centre back cover. I've seen him play twice there for Arsenal in friendlies already this summer, and it is a bit of a dodgy area for Arsenal.
So if he's keeping Song for that reason, that's one defensive midfielder down. Diaby we could say he sees as more of an attacking midfielder, so let's take him off the list too. That leaves us with Gilberto, Denilson, Flamini and Randall. Now Randall's only 17 and still developing, we don't know how good a player he'll become yet, so I can't see him being sold, and he doesn't really count as first squad anyway. Gilberto's definitely not going, Denilson is 19 and also still developing...so it seems like Flamini, at 23, would be the one to make way if Diarra moves. Only Flamini had the chance to move this summer and said he wanted to stay and fight for his place. And to be fair to him, he did well against Inter yesterday...I just think if Diarra moves it's unfair of Wenger to give him any hope of playing. Because even if we do consider Diaby attacking, he's still more likely to partner Fabregas if Gilberto, Denilson and even Randall are out than Flamini is.
Also, it's a bit of a...well, it's a bit embarrassing to be taking Chelsea's 4th choice defensive midfielder. I mean, I think he's genuinally a good player, but I actually agree with Mourinho and put Essien, Makelele and Mikel ahead of him.
In fact, when I look at the top 4...Hargreaves, Carrick, Essien, Makelele, Mikel, Mascherano, Sissoko...if any one of them was an arsenal player they'd be my first choice defensive midfielder. And I don't see how Diarra's going to change that.