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The Europa League semi-finals bring with them two sides who could well need victory -- Arsenal and Roma -- if they are to qualify for Europe against clubs with seasoned practitioners in this competition. Several Manchester United players were involved in the 2017 victory in Stockholm that handed the Red Devils their fifth major European trophy whilst Villarreal manager Unai Emery has already won this competition on three occasions with Sevilla. You have to go back to 2012 for the last time he lost a two-legged Europa League tie.

Let's make some predictions:

Roma's high line hands Manchester United the advantage

Paulo Fonseca might just acknowledge that his team are particularly disadvantaged to take on Manchester United, a side that relish opposition who play in the way the Serie A giants do. Roma will not compromise a playing style built on a high line just for one opponent, but they must know that this particular team is one of the best in the world at deploying rapier swift counter-attacks through sides.

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Of the Premier League's 'big six' teams -- i.e. those that generally face massed defenses sitting deep and challenging opponents to break them down -- United have by far the highest direct speed, advancing the ball 1.39 meters per second towards goal in an average move. By way of comparison that is nearly 21 percent faster than Chelsea and 36 percent faster than Manchester City. They may not always get opportunities to run in the open field, but when they do the likes of Marcus Rashford, Mason Greenwood and Bruno Fernandes burst into life.

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Roma's pass map in Serie A and Europa League games, reflecting the high line Paulo Fonseca wants his team to play with TruMedia

Roma, meanwhile, as the graphic above indicates like to keep the lines between their attack and defense exceptionally short. When it clicks the Giallorossi can trap opponents in dangerous areas, win the ball back and quickly advance to goal. But such a system leaves far more space in behind and with it room for error. It is notable that Fonseca's side are by far the runaway leader in Serie A in terms of errors leading to shots (14) and goals (nine). It is a similar story in the Europa League where only the eternal circus of the absurd that is Arsenal matches or betters them in those statistics.

"I think [when we've had problems] many times, it hasn't been because other teams created situations against us," Fonseca told ESPN this week. "It's because we made mistakes, losing balls in the first phase of play. And I think we paid more dearly for those mistakes than is normal, and that has been our biggest problem. Because yes, this type of game that we play can be risky, but in the long run I believe it is successful." 

Get their aggressive approach right and Roma may be able to hem United in effectively but one accurate ball over the top or a clumsy error at the back might be all it takes to turn this tie in the English side's favor.

Arsenal make life harder for themselves...

Because when do they not. By many statistical metrics Arsenal have been somewhere between the Premier League's fourth and sixth best team since Mikel Arteta's road to Damascus moment on Boxing Day when the Gunners beat Chelsea 3-1 and eased the pressure on their manager that was growing intolerable. Since Christmas they have the division's third highest expected goals (xG, a metric that assesses the likelihood of any shot resulting in a goal) and its third best goal difference.

However the difference between their xG and that of their opponents is sixth, the same as their position in a post-Christmas league table, which places as near to Burnley in 10th as second-placed Manchester United. Meanwhile their passage to the Europa League semi-final has been harder than their performances suggest it ought to have been, a dramatic win over Benfica and poor home results against Olympiacos and Slavia Prague meaning that every tie has felt in the balance at crucial intervals. In no small part the explanation for that is they keep shooting themselves in the foot with basic errors.

Dani Ceballos has been handing out goals to Europa League opponents in all too charitable fashion. Bernd Leno's howler against Everton was reflective of an increasingly skittish season between the sticks. Arsenal lead the Premier League in red cards this season despite having committed the fewest fouls.

There are factors to explain this error-prone season. It has not helped that Arteta has been unable to consistently deploy a defensive duo with Gabriel Magalhaes, David Luiz and Pablo Mari all spending time out through injury and illness. It was notable that the latter described having to change teammates at the back as "so difficult", adding "when you play a lot of games in a row it's more easy for you as a football player." Yet for reasons of fitness, form and fit that has not been an option available to many of the center-backs.

Arteta might also note that VAR has not been on his side, as in Friday's defeat to Everton where Nicolas Pepe was adjudged to be offside by a margin so fine it was hard to see how the decision to overturn a goal could be reached. The video assistants have done Arsenal few favors this season but it is hard to have much sympathy for those complaints when the Gunners are such masters of self-inflicted wounds.

..but their attacking firepower carries the day

Arsenal may have to dig themselves out of a hole in this tie but they will feel they have the quality in their squad to do so. The remarkable news that Kieran Tierney, David Luiz, Pierre-Emerick Aubameyang and Alexandre Lacazette are all in contention for the first leg offers a welcome boost to the Gunners' attack, which had previously looked like it might be lacking in firepower in comparison with Villarreal's.

Unai Emery will be able to call on one of the competition's form strikers in Gerard Moreno, who has formed a deadly partnership with Paco Alcacer that is in some ways reminiscent of how the Spaniard unlocked an Aubameyang-Lacazette tandem to fire Arsenal to the Europa League final two years ago. Add into the mix Samuel Chukwueze, Dani Parejo and Carlos Bacca as a possible supersub and it is little wonder that Villarreal sit comfortably second among the competition's remaining teams in terms of goals, shots and xG per game.

The problem is the team that sit ahead of them are Thursday's opponents. Arsenal are an offensive force in this competition, partly reflective an easy group stage bumping up their numbers but equally this is a team that have an outstanding collection of attacking talent that can score eight goals in three away knockout games with their talismanic forward Aubameyang either out of form or sidelined with malaria.

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How Arsenal and Villarreal strikers are performing in terms of their goal output and expected goals TruMedia

As the table above shows Aubameyang has endured something of a shooting slump in this competition and among players from these two teams only his fellow Arsenal striker Eddie Nketiah fares less favorably on Opta's shooting goals added, which compares xG from the shooting position with whether the shot actually hits the target. Indeed he is the fifth worst across the Europa League as a whole in this particular metric.

That should not necessarily be cause for panic at the Emirates Stadium when the matches after Christmas but before he contracted malaria on international duty saw Aubameyang get back into the positions where he was most effective with much greater regularity. Equally even if the club captain is off form Arsenal have plenty of other options to call upon. Nicolas Pepe has excelled in the Europa League as a scorer and creator, Alexandre Lacazette has a welcome habit of performing well in the biggest games when wearing red whilst the burgeoning young group of Emile Smith Rowe, Bukayo Saka and Gabriel Martinelli have proven to be fearless in the biggest moments.

There is more to their offensive output than just those at the top of the pitch and the return of Luiz and Tierney offers a far more interesting platform at the back. The former is at his best stepping forward and launching attacks from deep whilst Tierney is a devastating attacking weapon defined by excellent crosses and strong interplay with his winger. Of left-backs to have played over 900 minutes in the Premier League he ranks third in terms of key passes completed per 90 minutes.

The sheer weight of options Arteta has with key players returning significantly enhances his options and he has previously shown a willingness to exploit the options that come with being able to introduce five players off the bench. In the first leg draw with Slavia Prague he left it perhaps too late to unleash his flyers -- Pepe, Martinelli, Aubameyang -- after the more technical players that his side began the game with. However the Spaniard has proven to be a quick learner in his first job and if he gets his changes right in this tie it may be enough to swing a thrilling tie in Arsenal's favor.

CBS Research and TruMedia assisted with this article