Barca have won the competition in each of the last four years and have been present in all but one of the last eight finals.
Both teams have some injury concerns heading into the match, but some of the world's biggest stars will be on display at Camp Nou.
Here, Sports Mole has selected the best team from both squads, using only players available for this week's El Clasico.
Jasper Cillessen would have started this match between the sticks for Barcelona had he been fit, but the Dutchman will miss out with a muscular injury. As a result, Marc-Andre ter Stegen will play in the Copa del Rey for the first time this season. Madrid have two excellent goalkeepers in the shape of Thibaut Courtois and Keylor Navas, but Ter Stegen has taken his performances to a new level this season and the Germany international gets the nod in this team.
The defence is difficult to pick when considering the players available. That is not to say that both back fours have been watertight this season, but there are some big names that have to be left out. Marcelo's lack of form this season means that left-back is straightforward, with Jordi Alba enjoying an excellent campaign. Meanwhile, Los Blancos defender Dani Carvajal gets the nod over Barcelona pair Sergi Roberto and Nelson Semedo on the other side of the field as neither has been too impressive this season.
Raphael Varane is outstanding but his lack of consistency this season means that the Frenchman misses out in central defence. Clement Lenglet has played a lot of football for Barcelona this term due to the absence of Samuel Umtiti, but Gerard Pique has again been his team's outstanding central defender. Alongside him sits Sergio Ramos, who has scored a remarkable 10 goals from the back this season and is currently in wonderful form for the European champions.
It would be fair to say that Toni Kroos has not been at his best for Madrid this season and the Germany international misses out on this XI. Luka Modric does make it, but he is the only Los Blancos figure in the central three. Indeed, joining the Croatian are Barcelona pair Sergio Busquets and Ivan Rakitic. Arthur, Arturo Vidal and Casemiro all deserve mentions, but we are happy with a central three of Modric, Busquets and Rakitic in this particular team.
Further forward, Gareth Bale's injury problems mean that it is easy to leave the Welshman out. Vinicius Junior has been outstanding for Madrid in recent weeks, but he is just left out of this XI due to the form of teammate Karim Benzema, who scored his 18th goal of the season in Sunday's 3-0 win over Alaves. Benzema has four goals in four Copa del Rey ties this season, meanwhile, and is currently in wonderful form for the European champions.
Joining Benzema in the front three are Barcelona pair Luis Suarez and Lionel Messi. Suarez has 16 goals in 29 appearances this season, while Messi has registered 29 times in 27 matches in all competitions. The Argentine had been seen as a doubt for this game due to a thigh problem, but he is expected to start and rounds off what would be a formidable starting XI on current form.