Real Madrid assistant manager Aitor Karanka has said that the coaching staff are undecided over who will play in goal for Los Blancos on Sunday.
Diego Lopez has deputised for Iker Casillas since January, when the Real Madrid captain suffered a hand injury.
Casillas is close to returning from injury, but Karanka did not confirm whether the goalkeeper, who is Spain's record cap holder with 143 appearances, will return to the starting lineup.
"San Mames is special for any player," said Karanka.
"For Iker, for me, for Xabi Alonso, for Sergio Ramos. We still don't know who will play."
Real Madrid were drawn against German side Borussia Dortmund in yesterday's Champions League semi-final draw.
