An Atletico Madrid fan is in a stable condition in hospital after he was stabbed before Wednesday's 2-1 loss to Sevilla in the Copa del Rey.
A man arrested in connection with the incident is also reported to be an Atletico fan.
Police said the victim, a 22-year-old, was attacked near Las Musas metro stop by the Estadio Wanda Metropolitano.
They believe a confrontation took place among different groups within the hardcore element of Atletico's fanbase.
Madrid health officials said the man, who was stabbed in the leg, arm and back, was in a stable condition at the nearby La Paz hospital.
AS reported that he was a member of Frente Atletico, the club's main ultras group, and his attacker was part of a breakaway group called Suburbios Firm.
Spanish police said they had arrested a man they believed to have been responsible for the stabbing.
Reports said the arrested man had also been detained during an investigation into the 1998 killing of Real Sociedad supporter Aitor Zabaleta near Atletico's former Estadio Vicente Calderon home.
A court investigation into the death of Deportivo La Coruna ultra Javier Romero Taboada by the stadium in 2014 did not lead to any convictions.
Taboada was beaten with an iron bar and thrown into the river Manzanares, but a judge ruled that it was impossible to identify the guilty parties despite video footage of the incident existing.