Borussia Dortmund midfielder Konstantinos Karetsas was taken to hospital after suffering circulatory problems during Tuesday’s Champions League match against Villarreal.

The 18-year-old appeared to become unwell midway through the first half at Signal Iduna Park.

Karetsas played a routine pass to a teammate before signalling towards the referee and lowering himself to the ground without having been involved in a challenge.

Medical staff attended to him on the pitch for several minutes. He was then carried off on a stretcher and replaced by Ethan Nwaneri, bringing his Champions League debut to a premature end.

Dortmund issued an update while the match was still being played, confirming that Karetsas had experienced circulatory problems and was being transported to hospital for further examinations.

The club said that he was “doing well under the circumstances” but provided no further information about the cause of the incident.

Dortmund sporting director Ole Book later explained that there had been no indication of a problem beforehand and said the club hoped it would prove to be nothing serious.

Goalkeeper Gregor Kobel also expressed hope that his teammate would recover quickly and return to the squad soon.

The match was goalless when Karetsas left the pitch. Dortmund went on to record a 3-2 victory, with Serhou Guirassy scoring twice, but concern surrounding the young midfielder overshadowed the result.

Karetsas joined Dortmund from Genk during the summer and was making only his fifth appearance for the German club.

Further medical tests are expected to establish the cause of the circulatory problems. Until those results are available, there is no confirmed diagnosis beyond the information provided by Dortmund.

The club’s immediate focus remains on Karetsas and his recovery.