You're joking right?
Like they wanted to make a statement after losing to QPR?
People said Chelsea didn't have a chance against Napoli... look how that turned out, people said Chelsea didn't have chance against Tottenham... look how that turned out, people said Chelsea didn't have a chance against Barcelona... look how that turned out. Do you get it now? Don't be so fucking quick to write Chelsea off. Barcelona are the best side in World Football and if Chelsea can beat them two days after beating Tottenham 5-1 in an FA Cup semi-final then I'm sure Chelsea can (and will) beat Arsenal two days after beating Barcelona.
I know Chelsea had to work harder against Barca than Tottenham but that's where the changes will come in. EVERYBODY has played well under RDM (even Kalou and Mikel) and anybody in the squad will try their best against Arsenal. The only players I'd say that Chelsea will need against Arsenal from the Barca match are Cech, Terry and Mata. Cech's a goalkeeper, Terry is Chelsea's best defender and is capable of match-winning peformances when not even 100% and Mata was brought off, so they'll likely play.