Are Arsene Wenger's team genuine title contenders? Or will they be found out by the champions at Old Trafford? It's a stadium where Arsenal have struggled in recent years and where they were famously beaten 8-2 not too long ago.
But this is the Arsenal of Mesut Ozil, Olivier Giroud and a player re-born in Aaron Ramsey. The Gunners will believe they can win, and many are backing them to do so.
United remain in transition. With Sir Alex Ferguson gone, David Moyes' men are starting to put together some good results but are a long way from convincing the doubters.
Summer signing Marouane Fellaini has fallen short of what was expected, while United have looked vulnerable in defence and lacked creativity from midfield.
Could this be the afternoon Fellaini states his case? Or maybe it's a chance for Shinji Kagawa to explode at Old Trafford? Or will we see Robin van Persie bite the hand that used to feed him?
This is the place to come for live player ratings for United, to be entered at half-time and the end of the game.
De Gea—Fairly quiet half for United keeper.
Smalling—Neat and effective on United's right
Jones/Vidic—Yet to be penetrated by Arsenal's attack. Solid.
Evra—Excellent purpose down United's left. Doing the Leighton Baines role very well for Moyes.
Jones—In barnstorming form. Unlucky to be booked. Still lacks quality on the ball.
Valencia—Good movement and involvement.
Kagawa—Linked play well, yet to play a truly telling pass.
Rooney—World-class playmaking from Rooney. His passing and positional play have been immaculate.
Van Persie—One chance, one clinical finish. And some fine link play.
De Gea—Confident under the high ball, did nothing wrong.
Smalling—Dominant presence on United's right. Fine performance.
Jones/Vidic—Vidic subbed at half-time after head injury. Jones very impressive going back to central defence.
Evra—Another surging 45 from United's left-back.
Carrick—Understated, but effective.
Jones—Very impressive showing from Jones in midfield.
Valencia—Gave United a good outlet on the break
Kagawa—Still not at his best, but getting into his rhythm now.
Rooney—Unquestionably the best player on either side.
Van Persie—Neat link play as ever.