The Champions League kicks back into gear on Valentine's Day with Barcelona taking on Bayer Leverkusen and Lyon facing unlikely group stage heroes APOEL Nicosia. Both games air live on FOX Soccer and FOX Soccer Plus/2GO from 2:30 p.m. ET, while every Champions League and Europa League match is covered in real time on Twitter @FOXSoccerTrax .

On paper, Tuesday's games are ridiculous mismatches. Defending champions Barcelona face a Bayer Leverkusen side in free-fall, and most would tip a sub-par Lyon over Cyprus-based club APOEL. But appearances aren't always what they seem, and both of these matches have the possibility of being very uncomfortable for the favorites.

Barcelona are on a remarkable run, having just locked up a slot in their 12th major final (Copa del Rey) in just 3½ years under manager Pep Guardiola. They are unquestionably this era's greatest team, boasting the consensus best player on the planet, Lionel Messi. Their core group (Carles Puyol, Gerard Pique, Sergio Busquets, Andres Iniesta, Xavi Hernandez) helped Spain win the World Cup and have a chance to cement their place as one of the greatest European teams of all time this season.

So, what's the problem? Exhaustion.

Barcelona's starting to show signs of simply running out of gas. They've suffered a series of poor results and are probably out of the title race in Spain. The latest blow came Saturday when they fell at Osasuna 3-2 , allowing Real Madrid to move 10 points clear following Cristiano Ronaldo's hat trick over Levante this past Sunday .

While Messi remains one of the hottest scorers in the world, Barcelona have been forced to dip into their youth ranks to try to give the old guard a rest. The results have been mixed, with even their Copa del Rey home games against Real Madrid and Valencia proving tough to navigate. Barcelona eventually survived, but not with its usual flair. The old guard will be available Tuesday, with Cesc Fabregas, Iniesta and Xavi all expected to start.

Leverkusen aren't exactly in tip-top form either. They sit sixth in the Bundeslgia and have won only one of their last seven games. They will be without their influential winger Sidney Sam (thigh) and key striker Eren Derdiyok, who is out after cutting his foot on broken glass in his bathroom.

Michael Ballack will also miss the game with a calf injury, which is a mixed blessing: Ballack hasn't played since a falling out with the club's managing director, who branded the aging midfielder's transfer a "failure." Without Ballack, Leverkusen has struggled to find wins.

Leverkusen manager Robin Dutt has admitted the huge task his side faces. Barcelona averaged four goals per game on foreign soil in the group stages and was only given an honest test by AC Milan. This past weekend, Leverkusen only managed three shots on goal in a 1-0 loss to Bundesliga leader Borussia Dortmund , and now faces a team that has lost but one of their last nine. It's no wonder Dutt spoke of "miracles" in this sport.

There is one other factor in play, however: Spain, which has been dominated by the two giants, is now in an odd situation of sliding behind a smartly managed Bundesliga. No one doubts the quality of Spain's top clubs. But top-to-bottom, Germany offers a more competitive balance on a day-in, day-out basis.

Leverkusen, naturally, would love to get a chance to play in the finals on home soil (Munich hosts May's Champions League final). Being able to play at Bayern Munich's home turf will be an added bonus as well. Nonetheless, that may not count for much in this game, though it's worth keeping in mind that Dortmund had to work hard to win Leverkusen on Saturday. Bayer is never an easy out.

Lyon, you might recall, is fortunate to be here. They qualified in a last-gasp effort by routing Dinamo Zagreb 7-1 to pip Ajax on goal differential. The score line raised a few eyebrows at the time, but no irregularities were uncovered. Now, a team that can obviously score goals faces a side that has demonstrated an unwillingness to concede them.

No Cypriot side has ever beaten a French team. Goalkeeper Dionisios Chiotis is likely to be under heavy fire from a team stocked with explosive attacking talent. Bafetimbi Gomis and Lisandro Lopez will lead the French side out against a side that will play to defend and counter, with Nuno Morais trying to find lone striker Ailton up front.

Lyon's not impervious though. Remi Garde's men have shown serious defensive frailties, with even the normally calm Hugo Lloris showing frustrations by a defense that too often chases ghosts. This past weekend, 'Les Gones' were humbled 2-1 by an awful Caen side and will have to show more poise in Nicosia.

Wednesday's matches begin early, with Zenit hosting Benfica in St. Petersburg at noon ET, followed by Milan against Arsenal at 2:45 p.m. ET.