During the early part of the 20th century, players were often traded between Real Madrid and Barcelona.
However, as both sides started to battle it out for the top prizes in Spain, business between the two rivals became rarer and rarer.
That is not to say that some haven't made the leap down the years and if reports are to be believed, Barcelona are plotting a bid for Madrid's unhappy goalkeeper Iker Casillas.
So, with that potential transfer in mind, Sports Mole has looked back on five players that made the direct switch between La Liga's two biggest outfits and how they fared as a result.
1. Bernd Schuster - Barcelona to Madrid, 1988
The West German international was something of a favourite at the Camp Nou, having amassed over 200 appearances during his eight years with the Catalans. However, in 1988, he lost his hero status among the Barca faithful when he left for the capital. To make matters worse for his former club, he played a key role as Los Blancos won the La Liga title in 1989 and 1990. The midfielder then showed that he was not frightened to upset his new employers by joining local rivals Atletico Madrid. He returned to Real in 2007 as manager, but was sacked 12 months later despite having guided the club to the La Liga title.
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2. Michael Laudrup - Barcelona to Madrid, 1994
Such is the impression that the now Swansea City manager made on both clubs, Laudrup is still held in high esteem at the Camp Nou and the Bernabeu. In fact, he has been tipped to coach either side in the near future. He left Barca in 1994 after four successive league titles and a European Cup. At the time it was claimed that he had fallen out with Johan Cruyff, although the Dane has since denied that was the reasoning behind the move. He went on to inspire Madrid to the La Liga crown in his first campaign, making him the first player to win five Spanish titles in a row. He also shone as Madrid defeated Barca 5-0 that season.
3. Luis Enrique - Madrid to Barcelona, 1996
Among the scorers for Madrid during the aforementioned 5-0 demolition was midfielder Enrqiue, who had joined Real from Sporting Gijon in 1991. When the midfielder's contract expired in the summer of 1996, he forced a move through to Barca, making him a traitor in the eyes of the Madrid public. The former Spanish international revelled in such animosity, though, and often scored in El Clasico encounters. What's more, he would make a point of kissing the Barca badge on every occasion.
4. Luis Figo - Barcelona to Madrid, 2000
If Enrique is a hate figure for Madrid fans, then Figo is public enemy number one as far as their Barca counterparts are concerned. He had been a real cult hero in Catalonia following his 1995 arrival, playing a key role in seven trophy wins. That was instantly forgotten in 2000 when he left for Madrid in what was a reported deal worth around £45m. If he was in any doubt as to how he would be received upon his return to the Camp Nou, the answer was provided in the form of a pig's head, which was thrown at him as he prepared to take a corner. The Portuguese winger won two league titles with Madrid, as well as the Champions League.
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5. Javier Saviola - Barcelona to Madrid, 2007
No disrespect to the Argentine frontman, but this was a move that went a little under the radar. Having arrived at Barca in 2001 from River Plate, Saviola initially did well. That changed when Frank Rijkaard was appointed as coach and he was sent out on loan to Monaco and Sevilla. He returned for one more season with Barca, before going on to link up with Madrid on a free transfer in July 2007. Used mainly as a back-up striker, Saviola left for Benfica in 2009, although he did claim a La Liga medal in 2008.
