Barcelona midfielder Sergi Roberto insists Frenkie de Jong will be stronger for defeat to Athletic Bilbao.

Barcelona really struggled at San Mames and looked disjointed, with De Jong falling short of his pre-season level.

"Today was the first LaLiga [Santander] game and the level is different," Sergi Roberto explained.

"De Jong is a great player, but he just arrived and has to adapt.

"He had a difficult game because of Raul Garcia."