The lowdown on a meeting of two-time winners and an Arsenal side who have saved their best for this competition.
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Arsenal It has not been a great season for the Gunners but they have saved their best for Europe. The CSKA Moskva first leg and the home and away wins over AC Milan give a measure of what Arsenal can do – so too, though, the shock loss to Östersund and the second-leg wobble versus CSKA.
Atlético Eliminated at the UEFA Champions League group stage, Atleti have begun their pursuit of a third UEFA Europa League title with steely-eyed determination. København (5-1 on agg) and Lokomotiv Moskva (8-1) were summarily dismissed before a closer affair against Sporting CP.
Possible starting XIs
Arsenal Čech (CZE); Bellerín (ESP), Mustafi (GER), Koscielny (FRA), Monreal (ESP); Ramsey (WAL), Xhaka (SUI), Wilshere (ENG); Welbeck (ENG), Özil (GER); Lacazette (FRA)
Atlético Oblak (SVN); Juanfran (ESP), Savić (MNE), Godín (URU), Lucas (FRA); Correa (ARG), Saúl Ñíguez (ESP), Gabi (ESP), Koke (ESP); Griezmann (FRA), Diego Costa (ESP)
Mesut Özil, Arsenal The ex-Real Madrid playmaker has the ability to place a match under his spell, as CSKA learned in the last eight. Last month the 29-year-old reached 50 Premier League assists in record quick time.
Antoine Griezmann, Atlético The 27-year-old France ace is making a habit of picking up the scoring pace in the new year – his first 30 games this season brought 11 goals; he has hit 18 in the subsequent 20.
Ones to watch
Arsenal: Ainsley Maitland-Niles (midfielder), Reiss Nelson (midfielder)
Atlético: Jan Oblak (goalkeeper), Saúl Ñíguez (midfielder)
Arsène Wenger, Arsenal The Frenchman's decision to stand down at the end of the season, after almost 22 years in charge, means there are uncertain times ahead for the Gunners, but his players will be eager for the 68-year-old to add a first European honour to his 17-trophy haul with the club.
Diego Simeone, Atlético A fine midfielder capped 106 times by Argentina, Simeone has established a similarly formidable reputation as a coach. The 47-year-old took over at Atlético in December 2011, bridging the gap to Real Madrid and Barcelona and bringing five trophies into the Rojiblancos' cabinet, including this competition in 2012.
Why might they win it?
Arsenal The Gunners are on course for their worst Premier League finish since 1994/95, but every so often everything clicks into place and when that happens they are a match for almost anyone. Wenger's imminent departure may also provide a useful focus for the team and fans.
Atlético On paper Atleti are the best side in the tournament. Built on the bedrock of one of Europe's best defensive units, they have a midfield able to adapt to any situation and, in Griezmann in particular, a strike force that doesn't waste much.
Room for improvement?
Arsenal Defence. The Gunners have conceded just one goal less than 17th-place Swansea in the Premier League, and while they run a tighter ship in Europe there's often a sense of vulnerability. They have struggled away from home.
Atlético Atleti have a small senior squad so it doesn't take too many setbacks to have them reaching into their admittedly well-stocked youth ranks. Filipe Luís is a long-term absentee and when Lucas Hernández and Diego Costa were forced off in the quarter-final return at Sporting, the Rojiblancos struggled to make an impact.
Tell me something I don't know
Arsenal The north Londoners are the longest unbroken ever-presents in England's top flight, 99 years and counting, dating back to 1919. Atlético, in contrast, returned to the Liga after two seasons in the second tier in 2002.
Atlético There is a theory Atleti adopted their red-and-white stripes after a board member failed to find upgraded Blackburn kits during a trip to England in 1911. He instead bought Southampton shirts, with the Spaniards opting to keep their blue Blackburn shorts.