Season defining game: go through and there's still a chance to make this season a success. Lose and there will be serious questions asked of the manager/players.
• Valencia are undefeated in 11 UEFA Europa League home games, with wins in all of the last eight during which they have scored 22 goals and conceded just three. The last team to defeat them at Mestalla in this competition were a Premier League side, Swansea City racking up a 3-0 win on matchday one in the 2013/14 group stage.
• Of the 19 UEFA competition ties in which Valencia have lost away in the first leg, they have recovered to win on aggregate on ten occasions. When the defeat has been 3-1, however, they have lost all three ties. Indeed, the only time that they have come back from a first-leg away defeat of a margin greater than one goal was in the 2013/14 UEFA Europa League quarter-final, when they overturned a 0-3 defeat at Basel with a 5-0 home victory after extra time. That remains the biggest second-leg comeback in the UEFA Europa League knockout phase.
• Arsenal have won the first leg at home in 19 UEFA competition ties and have prevailed in 17 of them, most recently against Napoli in this season's quarter-final. The only two times that they have failed to qualify following first-leg victories in north London came after 2-1 scorelines, the first of them to Valencia in that 2000/01 UEFA Champions League quarter-final, the second also against Spanish opposition when they lost to Barcelona (1-3 away) in the round of 16 of the same competition ten years later.
Expecting the same team that played last week: Cech, AMN and that hippo Kolasinac to come back in after being rested against Brighton.