Manchester United face Schalke 04 on Tuesday at Veltins-Arena in the first leg of the Champions League semi-final, in a match many might wrongly assume will be a one-sided affair.

There are two credible reasons to doubt Schalke's ability to defeat a world-class club like Manchester United. First, the club is currently languishing in 10th place in the Bundesliga, and suffered a demoralizing loss this season to lowly Borussia Monchengladbach. Second, this club has never achieved anything remotely close to the type of success they're enjoying in this season's Champions League.

But then there are reasons to believe that Schalke has every much a chance to beat Manchester United as any prominent team. In the quarter-finals, Schalke absolutely dismantled defending champion Inter, netting seven goals against a traditionally strong defensive club. In the DFB Cup, the knockout German cup competition, Schalke found their way into the upcoming Final by knocking out Bayern Munich on their home field.

This somewhat obscure German club, which has had obvious struggles in the Bundesliga, thumped first phase opponents in Champions League by a combined scored of 10 goals to three.

Indeed, Schalke is puzzling.

Manchester United is generally in good health, and will have the luxury of knowing that they're closing in on the Premier League title.

But the Red Devils will be without Premier League leading goal-scorer Dimitar Berbatov, and may still have the aftertaste of losing to rival Manchester City in the FA Cup semi-finals.

Sir Alex Ferguson will want to pay close attention to some key Schalke players. Former Real Madrid striker Raul still has his goal-scoring form. In Champions League play, Raul has 5 goals in 10 games.

Schalke has among the best goalkeepers in the world in Manuel Neuer. Having caught the attention of a global audience with his solid performance in the 2010 World Cup, the German goalkeeper will be subjected to major transfer rumors, with Manchester United as one of his likely suitors.

A big question for Schalke is the health of two vital players: Dutch forward Klaas-Jan Huntelaar and defender Benedikt Howedes, who has been linked to Manchester United rivals Arsenal and Manchester City.

Playing at home, Schalke will likely come out with a burst of energy, as they face a Manchester United team that is the clear favorite.

Manchester United, for all of their glory, should certainly not overlook the successes of this German club.

Schalke is not a club to underestimate.

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