Ilkay Gundogan is an important part of Dortmund's success.
There are plenty of big stars to watch during the two legs of Borussia Dortmund vs. Real Madrid, but there are some lesser-known players who may have bigger games than Cristiano Ronaldo and Marco Reus.
Here are three underrated players to keep your eye on during the Dortmund vs. Madrid semifinal.
Ilkay Gundogan is simple but effective. You must have seen him on the field for Dortmund. He is usually the one setting up goals for Marco Reus and Mario Gotze.
Gundogan has good ball control and an ability to control the pace of the game.
He isn't flashy, and he isn't fast. He just gets the job done.
Throughout the match, you'll mostly find him sitting back and providing through balls for Gotze, Reus and Robert Lewandowski. He also has a nice shot.
He's not a player who receives a lot of praise for his abilities and contributions to Dortmund, but he is an instrumental part of the team's success.
Other European teams have noticed Gundogan's ability. He is a wanted man in both England and Spain.
Keep an eye on him in central midfield. Real Madrid will be looking to shut down his effectiveness.
What will happen in the first leg?
Blaszczykowski doesn't get the credit that he deserves. This is most likely because he doesn't start as many games as the other Borussia Dortmund stars. It may also be because it's pretty difficult to say his name. Just call him Kuba. It's far easier.
In the 28 matches that he has played for Dortmund this season, he has scored 13 goals. That isn't bad at all.
Compare that to Mario Gotze's numbers. In 35 matches, Gotze has scored 16 goals. Gotze gets high praise, but Blaszczykowski has been just as effective.
Look for the Polish captain on the field today. He may or may not start, but once on the field, he is instantly effective.
It's difficult to find an underrated player on Real Madrid. I'm not saying all of them are overrated. I'm simply pointing out that they are all superstars, and everyone knows their names. It's very difficult to single out a Madrid player as underrated.
But for these two matches against Dortmund, perhaps one player who may be underrated will be Fabio Coentrao.
Coentrao is a great player and has many admirers. But he missed Madrid's match over the weekend because of a muscle injury.
However, he will be back in the lineup for Jose Mourinho's side after Marcelo picked up an injury against Real Betis.
Dortmund may look to take advantage of the left side because of Coentrao's knock. Perhaps he isn't back to full fitness. We're not entirely sure.
Coentrao could have a good two matches against Dortmund. Madrid's defense will be without key members. Mourinho will put a lot of pressure on Coentrao to deliver, regardless of whether he is fully fit or not.
If he is fit, he will more than likely be very active in Madrid's counterattacks. He may even be able to steal a goal.