World football fans only have to wait a few more days until the drama of the UEFA Champions League finally returns.
Defending champions Bayern Munich are the favorites to win the sport's most prestigious club tournament and become the first repeat winners since AC Milan in 1990. With that said, an argument could be made that this year's field is more wide open than it's been in a long time, which should make for a thrilling tournament.
As we anxiously await the exciting fixtures scheduled for Matchday 1, let's take a look at three elite clubs on upset alert.
After a horrible defeat to Aston Villa at the beginning of the new Premier League season, the Gunners have won three straight matches in impressive fashion, including a 1-0 victory over North London rivals Tottenham.
But Arsenal was not among the lucky clubs during the Champions League group stage draw, grouped with last year's runner-up Borussia Dortmund, talented Italian side Napoli and French club Marseille, who the Gunners will face at the Stade Velodrome on Wednesday.
Marseille won't be an easy opponent for Arsenal. Elie Baup's men have begun their league campaign 3-1-1 with eight goals scored and four against. The French club also has a fantastic goalkeeper in Steve Mandanda, a goal-scoring winger in Mathieu Valbuena and one of Ligue 1's top right-backs in Rod Fanni.
When these two clubs were in the same group two years ago, Marseille earned a 0-0 draw at the Emirates Stadium following a 1-0 defeat to the Gunners on its home pitch. With a deeper and more talented squad since its last encounter with Arsenal, Marseille has a strong chance to pull of an upset and take a positive step toward the knockout stages this week.
Prediction: 2-2 Draw
Dortmund will face a much-improved Napoli squad on Wednesday as the German club begins its attempt to get back to the Champions League final.
The Italian club bolstered its attack in the summer transfer window with the acquisitions of two former Real Madrid players, striker Gonzalo Higuain and midfielder Jose Callejon. These additions add pace and goal-scoring ability to an already potent attack that also features world-class midfielder Marek Hamsik.
Napoli currently sits atop the Serie A table at 3-0-0 with nine goals scored and only two against. The Italian club is also in form on its home pitch with a 2-0-0 record, five goals scored and zero against.
When Dortmund travels to Napoli for its first European match of the 2013-14 campaign, it will need an A-plus performance to leave Italy with three points. The Stadio San Paolo is one of Europe's toughest venues to win at.
Prediction: Napoli 2-1
David Moyes will soon take charge of his first Champions League match as manager of Manchester United, and his club's first opponent is talented German side Bayer Leverkusen.
The Germans have started their new Bundesliga campaign in fine form at 4-0-1 with 11 goals scored and six against.
Meanwhile, United has been in a bit of a scoring drought with just two goals scored (one from the penalty spot) in its last three matches, two of which were against quality opponents Chelsea (0-0 draw) and Liverpool (1-0 defeat).
Which club has the best chance at an upset?
Luckily for Manchester United, this match will be played at Old Trafford, where the reigning Premier League champions are unbeaten this season.
With that said, the high-powered Leverkusen attack will be a difficult challenge for United because striker Stefan Kiessling, who led the Bundesliga with 25 goals last season, is in fantastic form with four goals during league play this year.
Without a strong defensive performance, United will start its new European campaign with a defeat.
Prediction: Leverkusen 2-1