A Manchester City supporter is in a critical condition following an alleged assault after Wednesday's Champions League game at Schalke, the club have announced.
City staff have stayed in Germany to support the fan, who is being treated in hospital.
A statement read: "Manchester City are aware of an alleged assault after the match at the Veltins Arena in Germany last night.
"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."
City won the first leg of the last-16 tie in Gelsenkirchen 3-2.
A Greater Manchester Police spokesperson said: "We are aware of an assault that occurred following the Schalke v MCFC fixture at the Veltins Arena in Germany last night.
"A British man is currently in hospital in a critical condition and we are working alongside the football clubs and German authorities to support their investigation and the man's family in any way we can.
"We would urge anyone with information to contact us on 101 or via Live Chat so that we can share intelligence with our colleagues in Germany."