Gonzalo Castro Is Borussia Dortmund Player with Most to Prove After Winter Break

The first six months of Gonzalo Castro's Borussia Dortmund career have been something of a roller-coaster ride. Signed from Bayer Leverkusen last summer for €11 million, per Transfermarkt, thanks to a release clause, the 28-year-old was supposed to replace Ilkay Gundogan in central midfield.

When Dortmund's No. 8 extended his contract in July, Castro seemed like the odd man out. Head coach Thomas Tuchel tried to get him involved, playing him at right-back in the UEFA Europa League qualifier against Odds BK in August—an experiment that lasted 45 minutes.

The man who made his professional debut for boyhood club Leverkusen at 17 years of age looked on his way to becoming a failed signing in the eyes of some impatient supporters.

There's no denying he turned things around, however. As the season went on, Castro became more and more important for Dortmund, and it's not a stretch to say he's one of the most important players as the team prepares for the second half of the campaign.

Therefore, it's not an indictment on his performances when we say Castro is the Dortmund man with the most to prove after the winter break.

As it stands, the 28-year-old is his team's top back-up at a number of positions. After selling Jonas Hofmann to Borussia Monchengladbach and agreeing to terminate Adnan Januzaj's loan deal this winter, the squad is short on wingers.

He's also the first option to replace either Shinji Kagawa or Ilkay Gundogan in the midfield triangle of BVB's 4-3-3.

This amounts to a major responsibility for Dortmund's No. 27, but on the evidence of the latter stages of the Hinrunde, he's up for the task.

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During the club's recent training camp in Dubai, Castro told the media, per Matthias Dersch of newspaper Ruhr Nachrichten he enjoys playing both positions. Looking at the busy schedule of the next few months, he also concluded the typical distinction between regulars and back-ups won't work.

It'd perhaps be more precise to say there won't be 11 regulars. Castro hasn't been a part of Dortmund's first-choice XI at any point in this season, yet he still has played in 23 of their 30 games across all competitions.

He is arguably one of the best 12th men in the Bundesliga, if one wants to call the top back-ups that. Coincidentally, he's also played the 12th-most minutes of all Dortmund players this season so far, per Transfermarkt.

That number is going to rise in the second half of the season unless Dortmund make a big signing in the transfer window—most recently, German tabloid Bild linked the Black and Yellows with FSV Mainz playmaker Yunus Malli (link in German, subscription required). Even if they do, Castro, who's scored four and assisted six goals this term, will be tough to beat out for playing time.

If he can show the form of the last two months of 2015 when the real football starts again at the end of January, no newly arrived player will automatically push him to the side. He topped our ranking of Dortmund's best players for the month of November, when we argued he's become more than a utility man or a first alternative when someone needs rest.

While it's always dangerous to read too much into practice games during training camp, Castro looked ready for the season to restart in the friendly against Eintracht Frankfurt on Tuesday. He assisted a goal in the 4-0 win and also scored an outrageous one himself, as you can see below—sadly, it didn't count as the linesman raised his flag.

If that's the Castro Dortmund fans will see in 2016, they're in for a treat. The 28-year-old, remember, was also involved in what many call the Black and Yellows' goal of the season so far, with his brilliant flick allowing Pierre-Emerick Aubameyang to open the scoring in the 4-1 win over VfB Stuttgart in November.

If Dortmund want to turn an already successful season into a great one, Castro's versatility and ingenuity will have to be on display even more in the coming months.

Lars Pollmann is a featured columnist writing on Borussia Dortmund. He also writes for Yellowwallpod.com. You can follow him on Twitter.