After being subbed off during the loss at Manchester United with a groin injury, Aaron Ramsey has been ruled out of this tie, so Theo Walcott could return to the starting XI on the right wing. The England winger was ill over the latter part of the weekend, though, and is a doubt.
Kieran Gibbs' recovery is going well, and he may be back soon enough, which many Arsenal fans will be happy about with Andre Santos failing to impress in his absence. Farfan had a lot of success over the Brazilian last time out and he could do again if Gibbs doesn't make it back in time.
Jack Wilshere has only just returned from injury, and while Arsene Wenger would normally be reluctant to use him only a few days after playing in the league, he is suspended for their next domestic match so he could feature here. Francis Coquelin will play if Wilshere doesn't make it.
Schalke's fantastic run of form, in which they won five games in a row - including the win at Arsenal - was ended at the weekend as they unexpectedly lost 3-2 at Hoffenheim. That was only their second defeat in all competitions this season, and the 90th minute winner will have taken the wind out of their sails somewhat.
Arsenal, meanwhile, have been out of sorts recently, losing to Norwich, Schalke and Manchester United in recent weeks, and while they have also won twice in that time, both wins were unconvincing to say the least.
Schalke thoroughly outplayed the Gunners when the sides played in London a fortnight ago, and back in Gelsenkirchen this time around, they will have the home advantage to boot. Arsenal will need to improve vastly if they are to get anything from this game, but with key players still missing, they could struggle again.
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