A Manchester City fan is in "critical condition in hospital" after an alleged assault following the Champions League match at Schalke on Wednesday night.
The club announced that City staff have stayed in Germany to support the family of the fan, who is being treated in hospital.
"Manchester City are aware of an alleged assault after the match at the Veltins-Arena in Germany last night," a club statement read. "The club are working with Greater Manchester Police and German Police to ascertain more information.
"Club staff have remained in Germany to support the family of an injured City fan who is currently in a critical condition in hospital.
"Anyone with information that can help the police should contact 101."
City won the first leg of the last-16 tie in Gelsenkirchen 3-2.
Two first-half penalties from Nabil Bentaleb cancelled out Sergio Aguero's early opener as the underdog hosts took a surprise lead into the break.
Nicolas Otamendi was shown a second yellow card before substitute Leroy Sane equalised with a fine free-kick with time still left for Raheem Sterling to score with virtually the last kick of the match.
The second-leg, in Manchester, takes place in three weeks time on March 12.
