A Deportivo La Coruna supporter has died after he was injured when dozens of rival fans clashed near the stadium before the club's La Liga match at Atletico Madrid on Sunday.
The 43-year-old Depor fan, who was not identified by name, had to be fished out of the freezing Manzanares river near Atletico's Calderon stadium and suffered cardiac arrest, hypothermia and head injuries, emergency services said.
Hospital sources later said he had died shortly after 2 pm local time after failing to respond to efforts to revive him.
Eleven other people were treated for mostly minor injuries, including one female police officer with a fractured hand.
Twenty people were taken into custody and a total of 100 troublemakers had been identified, police said.
Atletico and Spain's professional soccer league (LFP) condemned the violence and the LFP said it had wanted to suspend the game, which champions Atletico won 2-0.
Spanish media reported they had been unable to do so as it had not been possible to contact the Spanish soccer federation (RFEF) in time.
"I want to say that this has nothing to do with football," Atletico president Enrique Cerezo said in an interview with Spanish television recorded before the fan's death was announced.
"These are radical groups who meet up and these are the consequences," Cerezo added.
"I repeat that neither Atletico nor Deportivo have anything to do with these incidents, they are organised by radical groups who have their histories and their accounts to settle."
Depor president Tino Fernandez said clubs needed to do more to make sure such incidents were not allowed to happen.
"It's tragic news," he told Spanish TV. "I want to express our vehement opposition to violence."