The league leaders are just a point ahead of arch-rivals Real Madrid, who host struggling Racing Santander, and the build up to next weekend's 'clasico' at the Nou Camp has already begun.
To complicate matters, preparation time is short after the break for internationals and Barca also have to host Inter Milan in the Champions League on Tuesday in a game where defeat could end the defence of their European crown.
"It's vital to win in San Mames to give us confidence," Barca goalkeeper Victor Valdes told a news conference.
"It's always important to hang on to the top spot, not only because the following week we play Real, but because San Mames has always been a tough place for us to visit."
Bilbao, eighth, were hammered 4-1 by Barca in the King's Cup final last May, but the 'Lions' always provide opponents with a tough challenge built around the powerful figure of striker Fernando Llorente.
After sacking coach Juan Carlos Mandia last week, Racing have yet to appoint a full-time replacement but the visitors could benefit from a restless Bernabeu crowd as Pellegrini's side continue to struggle with inconsistency.
Real were booed from the pitch in their last home game after being knocked out of the King's Cup by third-tier Alcorcon.
"It's great news for everyone. His presence is vital and we have missed him," Real sports director Miguel Pardeza told sports daily AS. "We need him."
