Boca Juniors have not sold all of their allocated tickets for Sunday's Copa Libertadores final second leg against River Plate in Madrid, the Argentine club has confirmed to ESPN FC.
South America's football governing body, CONMEBOL, gave each of the teams based in Buenos Aires 5,000 tickets for the encounter at the Santiago Bernabeu.
"Boca has sold 4,600 tickets out of the 5,000 that were on sale," Boca press officer Rafael Veljanovich told ESPN FC on Thursday.
The remaining tickets will be returned to CONMEBOL.
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.
The game was originally scheduled to be played on Nov. 24 at River's Monumental stadium but an attack on the Boca bus caused it to be postponed.
CONMEBOL last week decided to have the game staged outside of Argentina for security reasons.
Madrid's local government said it expects between 20,000 to 40,000 fans from all over the world to arrive in the Spanish capital for the game this weekend, boosting the local economy by an estimated €55 million.
The town hall estimates that fans coming from abroad will spend €140 daily on food and entertainment.
"This event will generate direct and indirect revenue for Madrid for the travel to watch the game, also revenue as a consequence that the game and the image of Madrid will be transmitted to all the world," Madrid enterprise confederation president Juan Pablo Lazaro said as reported in El Pais.
CONMEBOL, meanwhile, has informed fans of the rules that must be followed while attending a game in Spain, stating that public disorder is prohibited, that possession of flares and weapons is not allowed inside the stadium and that banners inciting violence or terrorism are forbidden.
It has also stated that River fans will have to enter the Bernabeu stadium through the North Tribune while their Boca counterparts must do so through the South Tribune, with supporters only allowed seats in their allocated section of the stadium.