A night that was meant to mark a new beginning for one of Europe's leading young talents, Konstantinos Karetsas, instead ended with a medical scare.
Highly-rated prospect Karetsas endured a difficult evening as he made his UEFA Champions League debut for Borussia Dortmund against Villarreal.
Karetsas had little opportunity to showcase his technical quality before he was forced off midway through the first half.
The club confirmed afterwards that the 18-year-old had left the game due to a circulatory problem.
Konstantinos Karetsas’ Champions League Debut Cut Short by Circulatory Problem
Konstantinos Karetsas had been linked with several top European sides on the back of his displays for Genk, but it was Borussia Dortmund that paid €30 million to sign him.
The teenage attacking midfielder was named in the starting XI for Dortmund's first Champions League game of the season, making his debut in the competition.
He was heavily involved in the opening stages of the game before his dream debut took an unfortunate turn around the 25-minute mark.
The 18-year-old played a pass to a teammate before raising his hand to signal his discomfort to the referee, then lay down on the pitch without any physical contact.
He was replaced by Ethan Nwaneri after he spoke with the medical staff, before heading down the tunnel and to hospital for further tests.
The club subsequently confirmed that the player had experienced a circulatory problem and would undergo further tests in hospital.
"Konstantinos Karetsas had to leave the field due to circulatory problems. Kosta is doing well under the circumstances and is on his way to the hospital for further tests," the statement read.
The Greece international completed 85% of his passes while he was on the pitch, touching the ball 18 times. He also won a ground duel and drew a foul from a Villarreal player.
Borussia Dortmund Beat Villarreal After Karetsas Is Forced Off
Borussia Dortmund have endured a difficult run of injury news in recent weeks following Giannis Konstantelias' ACL injury and now Karetsas' circulatory issue.
Dortmund put the off-field concerns aside to begin their Champions League campaign with a win at Signal Iduna Park.
The game was scoreless when Karetsas left the pitch, and Dortmund had to wait until the second half to open the scoring through a Renato Veiga own goal.
Villarreal equalised in the 66th minute through Santiago Mourino, 13 minutes after Dortmund took the lead.
Serhou Guirassy added a brace to put the German side 3-1 up, scoring in the 80th and 85th minutes on his 100th appearance for the club. He scored a stoppage time own goal to ensure that the game finished 3-2 to his side.
