According to Belgian media outlet HLN, Borussia Dortmund youngster Karetsas, who went down and left the field during the match against Villarreal, did not suffer from a circulatory system problem. After hospital examinations, it was determined that the 18-year-old player was only experiencing dehydration.

Dortmund's home stadium suddenly fell silent. Around the middle of the first half, rising star Karetsas signaled toward the bench and then remained on the ground for an extended period, covering his face with both hands. The situation appeared concerning.
Karetsas started for Borussia Dortmund against Villarreal and made his Champions League debut. After joining from Genk, the Greek player had an outstanding start to the season and quickly established himself at the German top club, becoming a regular starter. However, serious concerns suddenly emerged over the condition of the high-profile signing.
Teammates, the referee and opponents all came over to check on the Greek player's condition. Amid warm applause from the entire stadium, he was carried to the sideline on a stretcher.
According to Bild, an ambulance arrived at 9:50 p.m. The outlet reported that Karetsas was carried out of the dressing room on a stretcher and taken to hospital, accompanied by his mother.
Borussia Dortmund later issued a statement saying: "Karetsas was forced to leave the match due to circulatory system problems. Given the current situation, he is in good condition and is now on his way to hospital for further examinations."
More details emerged afterward. Sources indicated that the issue was likely caused by dehydration; insufficient fluid intake can lead to dizziness, headaches and an increased heart rate.
Apart from that, Karetsas is in good physical condition.