When: Thursday, May 6, 20:00 GMT
How to watch: BT Sport
The pressure is on. Arsenal could potentially end the season with a major trophy and a spot in next season's Champions League.
On the other hand, they could end the campaign without any silverware and without any European football next season.
That second scenario would be an absolute travesty for a club of Arsenal's stature. The club's finances would also take a hammering.
Emery is a respected manager - don't get me wrong - but his spell at the Emirates ended on a sour note. This is his opportunity to showcase the qualities of a world-class manager and restore his reputation in the English market.
Last Three Matches
Villarreal 2-1 Arsenal (Europa League - April 29, 2021)
In the opening leg of this semi-final, it was Villarreal who raced to an early lead.
Goals from Manuel Trigueros and Raul Albiol gave the Spaniards a healthy advantage in the first 30 minutes.
Arsenal seemed shell-shocked and things soon got worse with Dani Ceballos being sent off.
The visitors eventually settled down and managed to net an away goal courtesy of a well converted penalty from Nicolas Pepe.
In the final minutes of the contest, Etienne Capoue was shown a red card as both teams ended the game with ten men.
Arsenal 3-0 Villarreal (Champions League - April 15, 2009)
Both clubs met in the Champions League quarter-final back in 2009 as Arsenal got the better of their Spanish opponents.
Theo Walcott, Emanuel Adebayor and Robin van Persie scored the goals as Arsene Wenger's men stormed to the semi-finals in style.
It was a painful defeat for Manuel Pellegrini's side who went down to 10-men in the 67th minute following the dismissal of Sebastian Eguren.
Villarreal 1-1 Arsenal (Champions League - April 7, 2009)
It was a much closer contest when the two sides met in the opening leg of the aforementioned quarter-final.
Marcos Senna delivered the opener as Villarreal took the lead in the 10th minute. Things then got worse for Arsenal as goalkeeper Lukasz Fabianski had to be replaced by Manuel Almunia on the half-hour mark.
Nevertheless, the Gunners found their feet and found an equaliser. Emanuel Adebayor put Wenger's men in a great position ahead of the rematch in London.
Last five head-to-heads
Arsenal wins: 2
Villarreal wins: 1
Arsenal goals: 6
Villarreal goals: 3
Arsenal need consistency
Mikel Arteta's men returned to winning ways last weekend with a 2-0 victory over Newcastle United.
The Magpies were missing a number of key players but for the Gunners this was simply about boosting morale and returning to winning ways.
Arsenal have won just three of their last ten games and are clearly lacking consistency. However, a win on Thursday could be the moment things begin to change for the London outfit.
Villarreal eye silverware
Villarreal have won three trophies in their history. One of them was the Tercera Division in 1970 and the other two came in Europe.
The club lifted the 2003 and 2004 UEFA Intertoto Cups - interestingly, the same number of European honours that Arsenal have won too.
Unai Emery is a Europa League master and is aiming to reach his sixth final. Villarreal are certainly well positioned and well equipped to seal the deal at the Emirates.
The man to watch in this game is Gerard Moreno. The Villarreal frontman has scored or assisted in all seven of his starts in this competition this season.
At the price of 2/1 (bet365) he's certainly worth a go.
From an Arsenal perspective, there's little to go at with the absence of Alexandre Lacazette. However, one man who could come up with the goods is Nicolas Pepe.
The youngster scored in the first leg and there's no reason why he can't do so again at the price of 21/10 (Unibet).