For both Arsenal and Tottenham, there is no bigger fixture on the Premier League calendar than the north London derby.
With both sides enduring tricky seasons so far, Sunday's meeting between the two always looked like being extra special. For Arsenal, victory would keep their top-four hopes alive and put a dent in Spurs', so you'd expect the Gunners to go gung ho for this one.
So, to see top scorer Pierre-Emerick Aubameyang dropped to the bench came as somewhat of a surprise.
While there's no denying that Aubameyang is yet to hit top form this season, he came into the game with four goals in his last four Premier League games. On that alone, he deserved to start, so there must have been something wrong behind the scenes.
Well, that's exactly what's going on.
Manager Mikel Arteta told Sky Sports News: "He was going to start the game. We had a disciplinary issue. We have drawn the line and we move on. He is on the bench.
"Obviously we keep it internal. We have a process that we have to respect for every game, and that's it. It's a decision made after evaluating everything, who Auba is and what he has done. That's it."
It's a huge decision from Arteta, who will know just how important this game is to Arsenal's season. Victory here could kick-start a real resurgence, but a defeat may well be the end of their campaign.
Aubameyang's absence from the starting lineup is obviously a major talking point, but the absence of fellow forward Gabriel Martinelli comes as just as much of a surprise.
The 19-year-old Brazilian, who has been glued to the bench for the past six games, does not even make the matchday squad this time around. If this is easing him back from his injury, Arteta looks to have gone a little OTT.
To add to the frustration, there was also no place in the starting lineup for £72m signing Nicolas Pepe, who has three goals in his last seven league games. The Ivorian was rested last time out in the 1-1 draw with Burnley, but there was seemingly no good reason for that as he's back on the bench this time around.
He's joined on the bench by Willian, who is in the best form of his Arsenal career with four assists in his last four games - the kind of form you might want for the biggest game of the season.