Osasuna defeated Real Madrid 2-1 in a LaLiga match, with goals from Ante Budimir and Raul Garcia del Haro. The loss gives Barcelona a chance to overtake Real Madrid in the title race.
Real Madrid said their participation in the tournament was never in question.
Real Madrid's La Liga title challenge was left hanging by a thread after a late Humberto Osorio header earned Real Valladolid a 1-1 draw and Cristiano Ronaldo suffered an injury on Wednesday.
Jose Mourinho has been on the ropes at times this season as Real Madrid's La Liga title defence stumbled but the Portuguese coach delivered knockout blows to heavyweight opponents this week that kept the Spanish club's hopes of silverware very much alive.
Barcelona players had their families and toddlers join in their La Liga title celebrations at the Camp Nou in Barcelona on Sunday.
The millions of fans around the globe who will tune in to watch Sunday's 'Clasico' in Barcelona could witness the death throes of Real Madrid's La Liga title challenge in their seventh match of the season. Defeat at the Nou Camp for Jose Mourinho's side, who are chasing a second consecutive title after ending Barca's three-year run as champions, would stretch the Catalan club's lead over their bitter rivals to 11 points.
Barcelona kept Real Madrid's La Liga title celebrations on hold for a few days at least with a crushing 7-0 victory at Rayo Vallecano on Sunday after Real had cruised to a 3-0 home win over Sevilla.
Holders Barcelona were drawn on Friday to play Real Sociedad in the quarter-finals of the King's Cup while Celta Vigo will take on Real Madrid.
Real Madrid's La Liga title hopes suffered a huge blow with a surprise 1-0 defeat at Osasuna on Sunday which left Jose Mourinho's side seven points adrift of leaders Barcelona.
At 80 million euros, 23-year-old Kepa Arrizabalaga will become the most expensive goalkeeper in football history, ahead of Liverpool's Alisson Becker.
The Modric family took refuge in a hotel near Zadar in 1991 when the war that followed the breakup of former Yugoslavia started and after Luka's grandfather was killed by Serb militia.
Cristiano Ronaldo and Gareth Bale will return to action for Real Madrid's La Liga game with Villarreal on Wednesday, coach Zinedine Zidane said.
Barcelona fall to shock Malaga defeat.
News of all that's transpired on and off the football field
Real Madrid's La Liga title bid took a dent after Zinedine Zidane's leaders were held to a 2-2 draw at home to Celta Vigo on Sunday, denied all three points by a late strike from Santi Mina. Lazio mounted a superb second-half comeback at the Olympic Stadium to beat Inter Milan 2-1 and move above Antonio Conte's side into second place in Serie A on Sunday.