Borussia Dortmund's teenage star Konstantinos Karetsas has been hospitalized with circulatory problems, the club confirmed. Karetsas, 18, was substituted 27 minutes into the club's Champions League tie against Villarreal on Tuesday night after slumping to the pitch.
The Greek attacker was observed kicking a ball back to a teammate before sitting down, prompting medical staff to attend to him on the field. He was subsequently stretchered off.
A club statement indicated that Karetsas was "doing well under the circumstances" and was en route to the hospital for additional examinations.
Earlier on Monday, German newspaper Bild reported that Karetsas had missed training due to fatigue. He joined Dortmund last month from Belgian side Genk in a reported £27 million transfer.
Karetsas's teammate, Giannis Konstantelias, also a Greek player, suffered an ACL injury on his debut earlier in the transfer window. This led Dortmund to loan in Ethan Nwaneri from Arsenal, who came off the bench in place of Karetsas during the match.
Dortmund secured a 3-2 victory over Villarreal in their Champions League opener. Serhou Guirassy scored twice for the Bundesliga side, who also benefited from a Renato Veiga own goal. Santiago Mourino had equalized for Villarreal earlier in the match, and Guirassy also scored an own goal in added time.