Danny Welbeck reportedly injured his arm in the warm up ahead of the game against Bayern Munich and was been replaced in the starting lineup by Olivier Giroud, however he was ill.
https://twitter.com/_AndyHa/status/839197534677516290
https://twitter.com/DannyWelbeck/status/839212401748754435
https://twitter.com/adrianjclarke/status/839198812006715392
The news was a massive blow for the tactics Arsenal would have worked on, relying on pace. That being said, Wenger had the chance of turning to Lucas whom most fans wanted to see and he didn’t. And after the first half, it seemed a good choice.