Real Madrid have not played in Salamanca for 21 years.
The last time Los Blancos travelled to the beautiful university city some 200 kilometres west of the capital was in April 1999, when John Toshack's side drew 1-1 with Union Deportiva Salamanca at the Estadio Helmantico.
UD Salamanca finished last in La Liga that season and in 2013, the club was dissolved due to huge debts and disappeared after 90 years of existence.
There are now two clubs in Salamanca and both play in the same group of Spain's third tier, the Segunda B.
Salamanca CF UDS, owned by a Mexican businessman and playing at the Helmantico, were formed from the remnants of UDS. They have also assumed the crest of the old club and their name is similar, too, although they were previously known as Salamanca Athletic, CD CF Salmantino and CF Salmantino UDS.
Unionistas is the city's other club. Founded by fans in homage to UDS (which features on their club badge), after those supporters had sought to save the old team, they are keen to avoid the type of model which led the previous version to bankruptcy. They play at Las Pistas, an athletics track next door to the Helmantico.
When the draw for the last 32 of the Copa was made, there was talk of switching the tie against Real Madrid to the Helmantico itself or even to the Santiago Bernabeu, but Unionistas stood firm and will play the match at Las Pistas, in front of just 4,000 fans.
Unionistas are currently 16th in Segunda B Group II, four points off the bottom of the table and four adrift of Salamanca CF UDS, in ninth.
