Konstantinos Karetsas collapses on Champions League debut for Borussia Dortmund against Villarreal

The scare came with the clock showing just 25 minutes played. Konstantinos Karetsas, Borussia Dortmund's young Greek prospect, played a pass to a teammate, raised his arm to call for the referee's attention, and moments later sank to the turf. All of this on his own Champions League debut, wearing the yellow and black jersey in a matchup against Villarreal.

The score was still 0-0 when play stopped and the medical staff rushed onto the field. Karetsas was treated lying on the pitch for several minutes before the decision was made to bring him off on a stretcher, visibly shaken but conscious. The image left everyone holding their breath, especially given that this is an 18 year old kid who had just begun to make his mark on Europe's top club competition.

The German club stepped in to explain what had happened shortly after, and that helped calm things down somewhat: it was not a cardiac issue, but rather a circulatory problem.

Konstantinos Karetsas had to leave the pitch due to circulatory problems. Kosta is doing okay under the circumstances and is on his way to the hospital for further tests.Borussia Dortmund

Karetsas was taken to a hospital in Dortmund to undergo the relevant tests and rule out any bigger complications. No definitive diagnosis is known at this point, but the club's message suggested the Greek winger was stable following the episode.

A season that began with excitement

Karetsas isn't just any name at Dortmund. He arrived this summer as one of the club's most eye catching signings, alongside fellow Greek international Giannis Konstantelias. The idea was for both young players to bring freshness and long term upside to the squad. Soccer, though, doesn't always stick to the script: Konstantelias suffered a torn ACL last month that has effectively ended his season.

Now the worry shifts to Karetsas, who was experiencing his first Champions League night as a Dortmund professional. There is still no word on the results of the medical tests or on his recovery timeline, so fans will have to wait for the club to share more information in the coming days. For now, what matters is that the player left the stadium conscious and, according to Dortmund itself, "doing okay under the circumstances."