The £87million Welshman has been nursing a slight calf problem and missed the 1-0 win over Espanyol in the Copa del Rey quarter-finals in midweek.
It is the latest of a number of frustrations for Bale, who has completed the 90 minutes just nine times in 30 competitive games this season.
If he fails to come through, former Academy player Jese - who stood in for Bale and scored the winner against Espanyol - could again feature.
Coach Carlo Ancelotti said: "If Bale is in the right condition, he will play.
"If he is not, then Jese may play. He's another option and he causes teams a lot of danger."
Real will travel in good form having won all of January's eight games unbeaten without conceding a goal.
Ahead of this weekend's round of games they are third in the table but just a point behind joint-leaders Barcelona and Atletico Madrid.
Fourth-placed Bilbao could provide a stern test, however, having won their last three league matches impressively.
Ernesto Valverde's men were beaten by Atletico Madrid in the Copa del Rey this week but confidence should still be high after beating Almeria, Real Valladolid and Osasuna by scorelines of 6-1, 4-2 and 5-1 respectively in La Liga.
Valverde said: "We are playing very well at the moment and doing some very good things, so I don't think this (cup loss) will cost us dearly."