Los Blancos are the defending champions after beating Atletico Madrid in last year's edition, and the winner of this tie will meet Barcelona in Sunday's final after they overcame Real Sociedad 3-2 in a penalty shootout on Wednesday.
Zinedine Zidane's men took to the field against Osasuna at the weekend despite the chaos caused by Storm Filomena, and the La Liga holders missed the chance to go top of the table after playing out a goalless stalemate at the El Sadar Stadium.
Here, Sports Mole looks at how Real Madrid could line up against Athletic, who have had a full week off after their clash with Atletico was postponed due to the weather.
Dani Carvajal was due to make his return to action here after missing out against Osasuna through suspension, but the right-back has sustained a muscular problem and will not make the cut on Thursday.
As a result, Lucas Vazquez - who is now in the final six months of his deal with the La Liga champions - will continue to deputise at right-back alongside Sergio Ramos, Raphael Varane and Ferland Mendy.
Casemiro and Toni Kroos are shoo-ins to start in the middle of the park, while Federico Valverde will be hoping to make headlines for all the right reasons this time after his controversial moment in the 2019-20 Supercopa de Espana final.
With Alvaro Morata racing through to score in extra time, Valverde scythed down the Atletico frontman in what many credited as a game-winning moment after 10-man Real eventually won in the shootout.
The Uruguayan midfielder could be preferred to the veteran Luka Modric for this semi-final clash, while Marco Asensio should start on the right flank with Rodrygo injured and Vazquez having to deputise in defence.
Luka Jovic is struggling with a muscular complaint but would not have been considered for a starting role over Karim Benzema, who netted a brace in Real Madrid's 3-1 win over Athletic last month.
Another goal for Benzema here would see him become the third-highest scorer in this fixture behind Telmo Zarra and Cristiano Ronaldo, and the fit-again Eden Hazard should keep his place on the left over Vinicius Junior.