Spanish police announced they have stopped a "most significant and dangerous" supporter from entering the country ahead of Sunday's Copa Libertadores final second leg between River Plate and Boca Juniors in Madrid.
The person who arrived at Madrid's airport on Wednesday evening was not named by authorities and has been sent back to Argentina.
Police said in a statement: "Police last night detected at Madrid's Adolfo Suarez Airport one of the most significant and dangerous Barras Bravas [ultra fans], who has a big criminal record. This person has been sent back to Argentina. Football is NOT violence."
Spanish-language news agency EFE reported the man deported as Maxi Mazzaro, a Boca Juniors supporter.
The South American football governing body, CONMEBOL, decided last week to have the game staged outside of Argentina for security reasons after the game which was scheduled to be played at River's Monumental stadium on Nov. 24 was postponed due to crowd trouble that left several fans and Boca players injured.
Argentina's ambassador in Madrid, Federico Ramon Puerta, said earlier this week that it will be difficult for the Barra Bravas from Boca and River to arrive in Madrid in time for Sunday's game.
Madrid police spokesman Serafin Giraldo described the security operation for the Copa Libertadores return leg as a "challenge" and estimated the cost of it at €150,000, with around 4,000 to 5,000 officers on duty.
Boca Juniors have not sold all of their 5,000 allocated tickets for Sunday's match, the Argentine club has confirmed to ESPN FC.
River Plate have reportedly sold even fewer tickets to their fans, with TyC Sports claiming just over 3,000 have been snapped up by supporters.