Athletic Bilbao forward Aritz Aduriz has warned his teammates that they have their work cut out to stop Sergio Ramos when they Real Madrid on Saturday.
Real Madrid captain Ramos has scored a number of crucial recent goals, and Aduriz told Spanish radio Cadena Cope that the defender was a big danger.
"I don't know who will have to mark Ramos -- but whoever does has a big challenge," he said. "We will try to mark him as best we can."
With defender Mikel San Jose serving a one-match ban, centre-halves Yeray Alvarez and Aymeric Laporte will have to keep a close eye on Ramos.
Aduriz was the active player to have scored the most headed goals in La Liga, with 45, before being overtaken by Real's Cristiano Ronaldo at the weekend.
He said of Ramos: "It really stands out that a player like him does the same thing over and over again. His capacity to attack the ball is overwhelming."
But he believes his side can pull off a shock result against league leaders Real, telling Marca: "Real Madrid is one of the best teams out there.
"We know in order to get a positive result we need to play a perfect game and have a good day. We can make life very difficult for them."
Teammate Inaki Williams said he believed the key to that would be stopping Ronaldo, telling AS: "He is lethal, ambitious and hard-working.
"But we are going through a very good spell. Madrid are playing for La Liga, but we need points to point to Europe."