A Deportivo La Coruna fan died on Sunday following clashes between supporters ahead of their 2-0 Liga defeat at Atleti.
The match at the Vicente Calderon went ahead despite the best efforts of the LFP (National Professional Football League), which confirmed that it tried to have the game postponed following the trouble outside the stadium.
Both teams and the RFEF (Spanish Football Federation) have since condemned the violence that preceded the match but the incident will cast a long shadow over Spanish football.
Atletico chief executive Miguel Angel Gil Marin said: "It's disgusting, that scum has no place in football. I just hope that they identify those responsible so they can't repeat actions as regrettable as these."
On the pitch, Atleti's thoughts must turn to Wednesday's first-leg clash with third-tier outfit L'Hospitalet at the minnows' 6,740-capacity home in Catalonia.
The prize for getting the better of their less-illustrious opponents will be a clash with city rivals - and semi-final vanquishers last season - Real Madrid, so coach Diego Simeone will be desperate to avoid a slip-up.
L'Hospitalet currently sit 13th in the Segunda Division B Group Three, but twice had to come from behind to earn a 2-2 home draw against basement club Real Zaragoza B on Saturday.
Coach Kiko Ramirez was critical of his players' performance in that match, but has urged his players to go out and enjoy their opportunity to pit their talents against the Liga champions on Wednesday.
"The match against Atletico Madrid, for me, is an occasion for the fans and for the players, they have to enjoy it," he said.
"I think it's an outlet. The result is not important, it is just important to have reached this point and to be playing against a big team.
"The players have to enjoy it because they deserve it, and I as a coach will work these coming days to forget the league and enjoy it, because [on Saturday] they were really bad."
Atleti will be boosted by the news defender Jose Maria Gimenez left hospital on Monday after suffering a blow to the head in Sunday's win over Deportivo.
Gimenez played the remainder of the game before going for tests and remained at Monteprincipe Hospital for overnight observation.
The 19-year-old is unlikely to be risked on Wednesday, despite being given the all-clear.
