The 22-year-old Casemiro played 25 games for Madrid in 2013-2014, but only started four of those. Competition for Real midfield places is heating up with the arrival of German World Cup winner Toni Kroos this week.

The Real-Porto accord includes an option to buy. Porto have already bought Dutch defender Bruno Martins Indi this week and taken attacker Cristian Tello on a two year loan from Barcelona.