Transfers between the arch-rivals are rare, with Javier Saviola the only player to have moved between the two clubs in the past 14 years when he left Barca for Madrid in 2007.
Sanchez, who starred up front for the Blancos between 1985 and 1992, suspects the Argentine is not pleased with his current deal, which runs until 2018 and contains a buy-out clause set at €200 million.
