John Terry v Theo Walcott
Olivier Giroud's sending-off in Zagreb is another reason for Wenger to start with Walcott. He has scored in his last two games, even if his finishing can be mixed, and his pace in the channels is something Arsenal could hope to exploit. Terry has never played with Baba Rahman so there may be space between centre-back and left-back.
Nemanja Matic v Mesut Oezil
Matic's major contribution this season was his superb strike in last week's 3-1 defeat by Everton. He has not protected the defence well enough and Chelsea have struggled against elusive attacking midfielders. That could afford an opportunity to Oezil, who is still to convince doubters that he delivers enough in the biggest games.
Diego Costa v Laurent Koscielny
Costa's brilliant volleyed goal against Maccabi was out of keeping with his bad-tempered but ineffectual displays this season. He has only one league goal, compared to seven at this stage last season. The athletic Koscielny is Arsenal's best defender. The question is whether he will be paired with Per Mertesacker or Gabriel Paulista.