German police have appealed for witnesses following the "violent clash" which left a Manchester City supporter seriously injured.
The Manchester City fan who sustained a "massive traumatic brain injury" following an incident inside Schalke's stadium is fighting for his life, police have said.
Polizei Gelsenkirchen issued a statement calling for witnesses in relation to an alleged assault that took place during Wednesday's Champions League match at the Veltins-Arena.
The injured fan was taken to hospital in a critical condition and members of City staff have remained in Gelsenkirchen to support the victim's family.
Fan's life in "acute danger", say German police
The man was said to have been knocked to the ground in a "violent clash" with two Schalke supporters at 10:50pm local time, during the closing stages of the Premier League side's 3-2 victory.
"In the scuffling, a 32-year-old Englishman was hit by a blow that caused him to fall to the ground," the statement read.
"In this fall, he suffered a massive traumatic brain injury.
"An emergency ambulance took him to the local emergency medical centre for treatment at a local hospital. There is currently acute danger to life.
"The police has set up a murder commission to investigate the incident and looks, in connection with this, for witnesses who can provide information on the facts and/or the perpetrators."
In a statement, Greater Manchester Police said: "We are aware of an assault that occurred following the Schalke v MCFC fixture.
"We are working alongside the football clubs and German authorities to support their investigation and the man's family.
"We would urge anyone with information to contact us on 101 or via live chat so we can share intelligence with our colleagues in Germany."