Real Madrid goalkeeper and captain Iker Casillas has received an offer from Portuguese side FC Porto, Spanish sports daily Marca quoted his agent as saying on Tuesday.

"An offer from Porto exists and Casillas is excited with that possibility. Now we have to wait to see what Real Madrid say," Casillas' agent Carlo Cutropia said according to the newspaper.

Real Madrid are reportedly trying to sign Manchester United goalkeeper David de Gea to the club and want Casillas to leave to avoid a potential controversy over which player should start.

Casillas, 34, has two years left on his contract with Real Madrid and, according to Marca, Real Madrid are willing to allow the player to leave as a free agent so he could sign a two-year deal with Porto.

Porto, coached by former Real Madrid and Spain goalkeeper Julen Lopetegui, will compete in next season's Champions League after finishing runners-up to Benfica in the 2014-15 La Liga season.

Lopetugui already has six Spaniards in his squad and both his assistant coaches are Spanish.

A World Cup winner and two-time European champion with Spain, Casillas has clinched five first division titles, three Champions League trophies and two King's Cup crowns since making his first-team debut with Real Madrid in 1999.