Real Madrid boss Rafael Benitez has branded Athletic Bilbao "a difficult opponent" ahead of their meeting at San Mames this week.
Los Blancos were beaten at Bilbao in La Liga last season, but will enter Wednesday's fixture having won three and drawn one of their four league matches this term.
Benitez has picked out Aritz Aduriz and Raul Garcia as the Basque side's two main threats, with Aduriz already netting nine goals in 10 games in all competitions this season.
Garcia, meanwhile, joined Bilbao from Atletico Madrid in the summer transfer window and has already found the back of the net for his new team.
"We know that Athletic are a difficult opponent, Madrid lost there last year," Benitez told reporters. "Raul Garcia and Aduriz are Athletic's references. We have to be very careful. It will be very complicated."
Real Madrid will enter Wednesday's match off the back of a 1-0 win over Granada at the weekend.
