Without a lot of injury problems, Borussia Dortmund head coach Thomas Tuchel's current first-choice XI largely picks itself.
Lukasz Piszczek has beaten out Matthias Ginter at right-back, while Sokratis Papastathopoulos pairs up with Mats Hummels in central defence by default—Sven Bender is still not available because of a knee injury.
Every other spot in the Black and Yellows' lineup is pretty much set in stone; Roman Burki, Marcel Schmelzer, Julian Weigl, Ilkay Gundogan, Marco Reus, Henrikh Mkhitaryan and Pierre-Emerick Aubameyang all more or less have a cast-iron guarantee to start.
The one spot that's up for grabs seems to be in Dortmund's midfield triangle, where Shinji Kagawa and Gonzalo Castro fight a duel.
On the surface, it doesn't look like a fair fight. The Japan international has spent over eight hours more on the pitch than the 28-year-old German for the club so far this season, per Transfermarkt.
Kagawa has produced eight goals and 10 assists across competitions, while Castro managed four and seven respectively.
There's little doubt Kagawa on his best form is the superior player to Castro. At peak performance, he's probably one of the best attacking midfielders in football. However, he's struggled to maintain his best form over an extended amount of time in his second stint with the Black and Yellows.
In November, we called the diminutive playmaker "undroppable." To that point, he had started 19 of his side's 22 games across competitions. It truly felt like Kagawa was back to full strength and to being the difference-maker he was during his first spell at Signal Iduna Park between 2010 and 2012.
Conversely, Castro hadn't played much of a role to that point. Until November, the former Germany international—his last of only five appearances for the DFB XI came in 2007—started only two league games. The start to the longtime Leverkusen man's Dortmund career was quite bumpy.
Since late in the year, however, the two competitors are on reversed paths. We ranked Castro as BVB's best player for the month of November, while Kagawa saw his playing time drop considerably in comparison to the earlier parts of the season.
Dortmund's No. 23 has only once played the full 90 minutes since November's international break, while Castro has started six games in that stretch.
Of course, there have been a few games in which both players were on the field together. Because of Castro's versatility, he's received some playing time on the wing.
However, it seems like Tuchel is reluctant to put him there, as evidenced by the fact the 28-year-old didn't get the start in place of an absent Reus against FC Cologne in December and FC Ingolstadt in 2016's first home game.
Dortmund's boss clearly thinks of Castro as a central midfielder first and foremost, and that puts him and Kagawa on collision course. Stylistic differences between the two mean Tuchel can pick specific spots for both, but Castro's performances warrant that he be considered the favourite to start most games at the moment.
Squawka's comparison matrix between the two players in the Bundesliga shows how the summer signing offers more of a threat on goal than Kagawa, who likes to sit in deeper pockets. Castro averages more assists per 90 minutes (0.59 to 0.40) and gets into better shooting positions himself, too (54 per cent shot accuracy to 37).
With his directness, the versatile midfielder connects well with Aubameyang especially, as was evident when he played a perfectly weighted through ball to the Gabonese against Ingolstadt on Saturday for the decisive second goal.
In the video below, skip to the 1:12 mark to see the assist.
On that day, Kagawa started in midfield but was almost invisible. Those 55 minutes might have been the Japanese's worst of the season, especially considering Dortmund needed so much more from him with Gundogan out because of an infection.
On the evidence of that game, the performances during the winter break and the last few weeks of the first half of the season, Castro has clearly overtaken Kagawa. He should relegate the Japanese to the bench for the time being.