Alaves edged out Celta Vigo on Wednesday to reach the final for the first time, whilst nine-man Barca had to survive a second leg onslaught from Atletico Madrid in midweek to make a fourth straight final.
However, Barca's quest for a second treble in three seasons faces more severe tests this week as a visit to Mendizorroza is followed by a Valentine's Day trip to Paris Saint-Germain on Tuesday in the Champions League.
Barca boss Luis Enrique has almost a fully-fit squad to choose from as Sergio Busquets and Andres Iniesta made their return from injury as second-half substitutes in midweek, whilst Neymar returns from suspension.
"We are delighted that Busquets and Iniesta have recovered," said Barca midfielder Ivan Rakitic.
"They are very important players and (having been out) they can give even more of what they bring to the team now."
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Madrid are in action for the first time in two weeks when they face rock bottom Osasuna, who are still without a home win all season.
Zinedine Zidane's men now face having to play half their league season in just over three months.
However, the break has allowed Zidane to recover a series of important players from injury with the visit of Napoli in the Champions League also to come on Wednesday.
Toni Kroos will be missing, though, through suspension.
Despite languishing eight points adrift of safety at the bottom of the table, Osasuna have shown signs of improvement since Petar Vasiljevic took charge in January.
Osasuna have taken the lead in each of their last three games and captain Oier Sanjurjo believes they are on the verge of turning their season around.
"We are strong. We have begun to show that we are competing," he said.
Third-placed Sevilla need to spoil Jese Rodriguez's home debut for Las Palmas on Sunday after joining his home town club on loan from PSG if they are to remain on Barca and Madrid's coattails in the title race.
Atletico hold the upper hand in the battle for the fourth Champions League spot, but six sides are separated by just seven points.
Two of them go head-to-head today as Espanyol host Real Sociedad, who can leapfrog Atletico with a win.
Atletico aren't in action till Sunday when they host Celta Vigo at the Vicente Calderon.
