Borussia Dortmund are reportedly keeping tabs on Real Madrid goalkeeper Iker Casillas.

The 32-year-old has endured a torrid time at the Bernabeu since losing his place in the first team to Diego Lopez.

Manchester United, Manchester City and Arsenal are thought to be among those interested in signing the Spanish international, although Los Blancos coach Zinedine Zidane has dismissed claims that he will leave the club.

However, Jurgen Klopp is believed to monitoring the situation as competition for places in Vicente Del Bosque's World Cup squad intensifies, according to The Mirror.

At the moment, Pepe Reina, David de Gea and Victor Valdes are all considered first-team regulars for Napoli, Manchester United and Barcelona respectively.