In the history of the Champions League and its predecessor, the European Cup, Arsenal and Atletico Madrid are the two teams to play the most games in the competition without ever lifting the famous old trophy. 

The Gunners, losing finalists in 2006, have played 223 games in Europe's premier competition without ever being crowned champions.

Atleti have played 190 and have been runners-up on three occasions, with two of those instances coming against fierce rivals Real Madrid in the last 12 years.

On Wednesday, the sides will face off in the first leg of their Champions League semi-final tie, with a place in the final – against Paris Saint-Germain or Bayern Munich – the prize awaiting the aggregate winners.

Ahead of the match, we dive into the Opta data to highlight the stories and players to watch.

What's expected? 

The Opta supercomputer views this first-leg matchup as extremely difficult to call.

Atleti were victorious in 35% of pre-match simulations, with Arsenal winning 37%, while the Gunners got back to the Emirates with a draw in 27.9% of our simulations.

According to the model's tournament predictions, Arsenal are favourites to win the tie, with a 72% chance of making the final, compared to Atleti's 28%.

The Gunners were also the tournament favourites ahead of this week's semi-final first legs, lifting the trophy in 36% of scenarios, compared to 35% for Bayern, 21% for PSG and 8% for Atleti.

Arsenal and Atleti have already met in the Champions League once this season, with the Gunners cruising to a 4-0 home victory in the league stage in October.

That was Atleti's joint-heaviest defeat in the tournament (they have lost by four goals on five occasions in total), but the teams' only other European meetings came in the 2017-18 Europa League semi-finals, and Los Colchoneros won 2-1 on aggregate (1-1 away, 1-0 home).

In addition, when playing at either the Vicente Calderon or the Estadio Metropolitano, Atleti have never lost at home to an English side in a Champions League knockout-stage match.

They have tallied three wins and three draws in six such matches, all of which were against different clubs (Chelsea, Leicester City, Liverpool, Manchester United, Manchester City and Tottenham).

This will be the 16th European Cup or Champions League semi-final tie between Spanish and English teams – the sides from England have progressed in nine of the previous 15 (60%), and in four of the last five (the exception being Man City versus Real Madrid in 2021-22).

Arsenal flagging or ready for final push?

Arsenal may have wobbled in recent weeks, but as we prepare to enter the month of May, their hopes of a Premier League and Champions League double remain very much intact.

The Gunners looked physically spent at the culmination of Saturday's 1-0 win over Newcastle United at the Emirates Stadium, though, and they cannot afford to show any signs of fatigue against a side that dumped Barcelona out in the quarter-finals.

Mikel Arteta's side have been heavily criticised for their attacking output lately, but the Spaniard would, given his pragmatic nature, likely take a first-leg draw.

If Arsenal avoid defeat, they will match their longest-ever unbeaten run in the European Cup or Champions League, having gone 13 matches without defeat between March 2005 and April 2006, a streak that ended with their final defeat to Barcelona.

Defensive solidity has been Arsenal's trump card, particularly in this tournament.

In the 22 Champions League games that David Raya, William Saliba and Gabriel Magalhaes have started together, Arsenal have only conceded 11 goals (0.5 per game) and kept a clean sheet on 13 occasions (59%).

But as the competition intensifies, Arteta must find a way to get more out of his misfiring attack, and that is why Bukayo Saka's return to fitness could be a timely boost.

Saka is perhaps unlikely to start on Wednesday, given he only made a brief appearance off the bench against Newcastle, but he is back in contention following an Achilles injury.

Arsenal have averaged 2.6 goals and 2.3 expected goals (xG) per game when Saka has played for them in the Champions League this season (eight matches), compared to just 1.5 goals and 1.8 xG per game when he has been absent (four matches). 

Saka has produced more successful pull backs (three) in the competition this season than Gabriel Martinelli, Noni Madueke and Leandro Trossard combined (two), so his comeback should be a boost for Viktor Gyokeres, who may be recalled in attack after Kai Havertz was withdrawn against Newcastle. 

Alvarez to dent Arsenal dreams again?

Many expect Wednesday's game to be a tight, hard-fought affair, given Arsenal's defensive prowess and Diego Simeone's own reputation for instructing his team to sit deep.

Indeed, when facing opposition build-up moves, Atletico Madrid have the ninth-highest percentage of time spent in a defensive low block (20.4%) in this season's Champions League, out of all 36 teams involved in the league stage. 

Simeone's side also rank among the bottom 10 sides for percentage of time spent in a high defensive block (26.4% – 27th).

However, they pick their moments to apply pressure, averaging 374 high-intensity pressures per game in the Champions League this season, the fifth-most by any team. Their average is almost 100 more than any of this year's semi-finalists, with Arsenal the closest side to them (281 per game). 

And while both Simeone and Arteta may be cautious, Atleti will be keen to take a lead to the Emirates for next week's second leg, and unleashing the star quality of Julian Alvarez could help them to do so. 

The Argentine, who helped Manchester City pip Arsenal to a pair of Premier League titles in 2022-23 and 2023-24, has already broken the record for the most goals by an Atleti player in a single European Cup or Champions League campaign, netting nine times in 2025-26.

He also leads all players in the 2025-26 edition for total high-intensity pressures (853), as well as boasting the most per 90 minutes (70 – minimum 500 minutes played).

PLAYERS TO WATCH

Atletico Madrid – Antoine Griezmann

Though Alvarez may be the face of Atleti's present, one of their all-time greats could line up alongside him, having provided plenty of Champions League heroics in the past.

Griezmann, who will be desperate to lift silverware with Atleti before leaving for Orlando City at the end of the season, has been directly involved in 24.2% of Los Colchoneros' all-time goals in the Champions League (56/231 – 40 goals, 16 assists).

That is the highest percentage by any player for a team who have scored 100+ goals in the competition's history, just ahead of Lionel Messi for Barcelona (24.1%).

Arsenal – Viktor Gyokeres 

Half of Gyokeres' goals for Arsenal in the Champions League (2/4) came in the second half of their 4-0 win against Atleti last October. 

However, the Swede has not scored in any of his four knockout-stage games in this edition and has had just six shots across those matches – 28 players have had more attempts since the start of the round of 16.