Eighteen-year-old Konstantinos Karetsas slumped to the turf 25 minutes into his Champions League debut for Borussia Dortmund against Villarreal
Borussia Dortmund confirmed Karetsas left the pitch due to circulatory problems and was taken to hospital for further tests
The German side noted that Karetsas was doing well under the circumstances after receiving on-pitch treatment and being stretchered off