Barcelona midfielder Xavi Hernandez believes Real Madrid will be badly affected by the loss of goalkeeper Iker Casillas to injury.
Casillas, the Madrid captain, has been ruled out for around three months with a hand injury, leading the Spanish champions to bring Diego Lopez back to the club from Sevilla.
Casillas has not enjoyed his best season at the Bernabeu, with coach Jose Mourinho dropping him in favour of Antonio Adan amid reports of tension behind the scenes, but Xavi feels Madrid will suffer in his absence.
"His injury is a problem," Xavi told reporters. "He is the soul of Madrid and their captain. It is a significant injury for Real Madrid and the national team."
Xavi has a well-publicised friendship with his fellow Spain star - the midfielder's father claimed in the summer that their relationship had caused problems with Mourinho - and he said he continues to speak to him on a regular basis.
"I talk to him a lot," he said. "We message each other, send encouragement. I have given him encouragement at moments, like when his coach saw fit not to start him in the team.
"That took me by surprise. It is amazing that suddenly a goalkeeper who has played for many years then does not play. That surprised me, but it is a topic for them. These are complicated issues, it is not for me to comment. They will be two months without Iker, who is a cornerstone at Madrid and for the national team. Aside from that I cannot comment."
Casillas will miss the Copa del Rey semi-final meeting with Barcelona, and Madrid are also contending with off-field issues, but Xavi feels they still represent a notable threat.
"They look to not be having a good time with the press or institutionally, but now we will face them in the semi-final and they are a complicated opponent who could eliminate us," he said.