Here's a football trivia question: What can London boast that Barcelona, Munich, Milan or Lisbon cannot match?
The answer is that none of those cities, the home to some of Europe's most successful clubs, can claim to have an unbroken run of qualification for the Champions League group stage stretching back to the last century, but London can.
Ever since Arsene Wenger's Premier League and FA Cup Double winners qualified for the Champions League in 1998, London has had at least one club in the group stage every season. Only Madrid and Manchester have longer unbroken sequences, with multi-club cities such as Athens, Istanbul and Moscow also failing to produce at least one group-stage representative in every season of the 21st century.
But London is in danger of surrendering its record of being a Champions League staple this century. The 2020-21 Premier League season is past the halfway stage and West Ham United are the leading light in London's attempt to have at least one team at Europe's top table. It's perhaps a sign of the decline of the capital's traditional powerhouses -- Arsenal, Chelsea and Tottenham Hotspur -- rather than the rise of David Moyes' team, who are fifth, four points behind fourth-placed Leicester City.
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Sunday's 3-1 defeat at home to Liverpool was humbling reminder to the Hammers, however, of the strides they must still make to become a team capable of sustaining a push for European qualification; few at West Ham would expect the London Stadium to be hosting Champions League football next season. Moyes' team are making progress, and a place in the Europa League would be regarded as a success.
But it is a different story at Arsenal, Chelsea and Spurs. For each club, missing out on the Champions League would be a major blow, both in terms of finances and prestige. It would also make it much harder for them to recruit top-level players capable of closing the gap on the Manchester clubs and Liverpool in the seasons ahead.
On Thursday, Spurs host Chelsea in a crucial clash for the ambitions of both. Spurs are six points behind Leicester, albeit with a game in hand, following Sunday's 1-0 defeat at Brighton, with Chelsea on the same number of points having played one game more than Jose Mourinho's team. And Arsenal, despite five wins and two draws from their last seven league games, are still eight points off the Champions League pace in 10th.
Can any of London's big three find a way to break into a top four that is already beginning to pull clear? Manchester City and Manchester United seem on course to qualify for the Champions League, as do defending champions Liverpool, so perhaps London's only hope is for Leicester to suffer the same late season slump that cost them a top-four finish last season.
Arsenal have most to do, but they have at least found form and purpose under Mikel Arteta. In December, the Spaniard's future was being questioned after overseeing the club's worst start to a season since 1974, but the manager's decision to back the promise of youngsters Emile Smith Rowe and Bukayo Saka has been rewarded with the unbeaten run that has seen all players -- young and old -- start to deliver.
Absent from the Champions League since 2016-17, Arsenal's failure to secure the major finances that come with playing in UEFA's elite competition continues to hamper their efforts to rebuild in the post-Arsene Wenger era. Their early-season form has almost certainly left them with too much to do, though, and they are facing another season outside the Champions League.
Spurs and Chelsea can still close the gap, and the outcome of Thursday's game at the Tottenham Hotspur Stadium will give an indication as to which of them is most likely to threaten Leicester's grip on fourth. Chelsea have already made their move in terms of shaking things up at Stamford Bridge by sacking manager Frank Lampard and replacing him with former Borussia Dortmund and Paris Saint-Germain coach Thomas Tuchel.
Having spent more than £220 million on new signings last summer, Chelsea owner Roman Abramovich sanctioned Lampard's dismissal knowing that Tuchel has time to turn the situation around and find a way to inspire Timo Werner and Kai Havertz to find the attacking quality that prompted their recruitment. In two games so far under Tuchel, Chelsea have banked four points and kept two clean sheets, so there are early signs of progress. But that can be undone with a defeat at Tottenham.
It is Spurs who should be the favourites to keep London's flag flying in the Champions League, however. Mourinho has the Premier League experience and a proven track record in the Champions League. Spurs also have a game in hand which, if they win it, will take them above West Ham and move them three points behind Leicester. But Spurs have suffered a dramatic loss of form in recent weeks, with just two wins from their last nine league games. Since surrendering top spot with a 2-1 defeat at Liverpool on Dec. 16, Mourinho's team have dropped like a stone, scoring just nine goals in seven games.
With Harry Kane now sidelined with an ankle injury and Gareth Bale failing to show anything like his best form since arriving on loan from Real Madrid, Spurs risk running out of steam, and goals, just as the top-four race begins to intensify.
Just like Arsenal before them, Spurs need Champions League football to finance their new stadium. Failure to qualify again would raise question marks over the club's ability to hold on to the likes of Kane and Son Heung-Min. But right now, none of London's heavyweights look to be safe bets to qualify for the Champions League, and the city's unbroken run in the competition is at risk.