Both teams have their problems but should relish a return to a competition that brings the best out of them.
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- Unai Emery faces Valencia side he coached from 2008 to 2012
- Arsenal have won just one in five against Valencia (D1 L3)
- Shkodran Mustafi, Francis Coquelin, Gabriel face former sides
- Fitness tests for Pierre-Emerick Aubameyang, Nacho Monreal
- Aaron Ramsey ruled out for season with hamstring injury
Reporter's view: After three straight Premier League defeats, Arsenal will be glad to find themselves in the relatively comforting surrounds of the UEFA Europa League again, having sparkled against Napoli in the last round. Injury has ended Aaron Ramsey's season, but the contribution of Pierre-Emerick Aubameyang and Alexandre Lacazette over the two legs against Napoli will surely mean they are used together again as Arsenal go for goals to take to the Costa Azahar.
Andy Brassell, Arsenal reporter
Arsenal: Leno; Papastathopoulos, Koscielny, Monreal; Maitland-Niles, Xhaka, Torreira, Iwobi, Kolasinač; Aubameyang, Lacazette
Out: Bellerín (knee), Holding (knee), Ramsey (hamstring), Denis Suárez (groin), Welbeck (ankle)
Doubtful: Aubameyang (sinus), Monreal (calf), Özil (foot)
Valencia: Neto; Piccini, Roncaglia, Garay Gabriel, Gayà; Guedes, Parejo, Wass, Soler; Rodrigo, Mina
Out: Cheryshev (knee), Coquelin (suspended), Kondogbia (thigh)
Ainsley Maitland-Niles v Gonçalo Guedes: Guedes carries much of Valencia's attacking threat. This time last year he was running on empty, but now it's quite the opposite now. Fit, full of power and chutzpah, he's beguiling to watch. Not only super-quick down the left wing, he now drifts into inside-left and second striker positions. Hard to handle, and the attack-minded Maitland-Niles will have to be on his guard.
Graham Hunter, Barcelona reporter
Where to watch
Unai Emery, Arsenal manager
We have big ambition and motivation in this competition. It's a semi-final and it's going to be difficult. At the beginning of the season we knew it was going to be very difficult to finish in the top four [in the Premier League]. We will continue trying, but not look at the table – the Europa League is a big motivation for us.
Marcelino, Valencia coach
Our point of reference is Arsenal's quarter-final win against Napoli. Make no mistake: we're up against a great team, with great power and on their pitch. It will be very, very difficult for us ... and for them too, I hope. I expect a very difficult game against a side with a lot of depth, talent and speed, very quick in the transition. We have to avoid losing the ball in our half.