It is the second matchday of the competition, and here's what to look out for over the two days of action.
United travel to Madrid, Viking face stern Bayern test
As always with the Champions League's League Phase, 18 games means there is enough narrative to go around.
In the early kick-off, Sabah make their home bow in what could be one of their most winnable games of the eight. The underdog side from Baku welcomes Slavia Prague to the Azeri capital, with both sides searching for their points of the campaign.
It has not been an easy ride in the Champions League for the Czech champions in recent times - they are winless in their last 20 outings, and lost narrowly to Lens in the opening matchday after a five-goal thriller.
Rwandan international Joy-Lance Mickels could be the spark for Sabah - he has netted four of their six goals in the competition to this point.
Elsewhere on Tuesday, Manchester United face a tricky trip to the Spanish capital, where they will face Atletico Madrid.
Atleti have been a thorn in the side of many in the Champions League recently, making it to the semi-finals last season, losing to beaten finalists Arsenal.
Incredibly, the tie with the Red Devils is their sixth game against English opposition in the competition from their last eight. Diego Simeone seems to enjoy the battle too, and it will be a tough test for Michael Carrick's side, who have only won twice this season in all competitions.
Viking, like Sabah, will play their first-ever Champions League game at home on Tuesday as they host Bavarian behemoths Bayern Munich.
Recently, the Norwegian side have turned their ground into a fortress, winning their last 11 in a row. A quirk for this fixture is that they won't be playing at home at all; instead, Stavanger's Lyse Arena will be the venue for the game.
Flashscore has given Viking just a 6% chance of winning - can they shock the continent and pick up a famous win?
Arsenal face French side Lille at the Emirates Stadium, looking to make it two from two in the Champions League, whilst if you are looking for some nostalgia and perhaps a shock too, look no further than Galatasaray vs Barcelona from 21:00 CET.
The Turkish giants have made a habit of pushing Europe's best hard at home, whilst the free-flowing Catalans have looked irresistible so far this season. This has all the hallmarks of an entertaining affair where we could see an upset.
UEFA Champions League
The UEFA Champions League pits the top clubs in Europe against each other in the continent's most prized cup competition. The 2026/27 edition follows the same format as last season, with 36 teams participating in the league phase before the top 24 progress to the knockout rounds. Want to know more? Follow the links below!
All you need to know | Latest Champions League news | The full Champions League draw
City play first home game since charges, Roma face litmus test
All eyes will be on the Etihad Stadium on Wednesday night, when Manchester City take to their field for the first time since being charged by the Premier League with financial mismanagement.
They came through their first test against Liverpool at the weekend with flying colours after a 3-0 victory, and now they head home for perhaps the hardest game in the Champions League.
Reigning champions PSG will be their opponent, and much will be made of what happens off the pitch rather than on it. How will Manchester City's wider fanbase treat their current stars, and will PSG's travelling support make any reference to it throughout the evening?
With so much still hanging over City's heads, every game of theirs will be must-watch, and the clash between Europe's most aesthetic sides could provide plenty of fireworks too.
Liverpool will look to recover some form in Austria as they face Champions League new boys LASK in one of two early kick-offs, whilst Aston Villa take on Fenerbahce.
Elsewhere, another English ground will host a game on Wednesday, but it will be a different type of affair than normal.
Stamford Bridge, home of Chelsea, was picked to host Shakhtar Donetsk's home games this year, and the Ukrainian side get their first taste of English hospitality this week, as they take on AEK Athens.
Read more: How Kevin De Bruyne is ready for European redemption.
Meanwhile, over in Italy, Jose Mourinho is preparing for a reunion, as he takes his Real Madrid side to the Stadio Olimpico to take on former club Roma.
Mourinho became a cult hero in the Italian capital after winning the UEFA Conference League in 2022.
Under current boss Gian Piero Gasperini, the Giallorossi are dreaming of even more silverware this season, after an unbeaten start to the campaign. Donyell Malen has been particularly important, netting six times in seven games.
Mourinho's Madrid have already tasted victory against Italian opponents this season after they beat Inter 2-1 in the opening week, but if Roma can overcome their former boss, it could provide a huge shot in the arm to their ambitions this season.
Follow every kick of the Champions League with Flashscore, and you can also find all the best news from the competition right here.
Josh Donaldson is a Global Senior Editor and International Football Specialist for Flashscore. From the UK, now living in Prague, Josh specialises in football and cycling and can be found at an obscure ground watching games or on his bike. You can follow Josh on X and read his articles here.
