Ole Book provides an update on Konstantinos Karetsas

"He's doing well under the circumstances. Further examinations are underway; we want to get to the bottom of this," said Ole Book on Thursday regarding Konstantinos Karetsas 's health.

Only once the further examinations are complete will there be additional updates on the 18-year-old. However, the BVB sporting director emphasizes: "It's clear that our top priority is the health of the person and the players. He won't be playing this weekend."

Konstantinos Karetsas took the field for Borussia Dortmund in the UEFA Champions League for the first time on Tuesday evening during the home game against Villarreal CF. Midway through the first half, the 18-year-old suddenly complained of circulatory problems and was substituted in the 27th minute. Karetsas was then taken to the hospital for further examinations.