Madrid now lead by two points and Los Blancos still have a game in hand after their match away to Celta Vigo in February was postponed due to storm damage at the Galicians' Balaidos stadium.
REAL MADRID INJURIES
Raphael Varane and Pepe are both out injured, so Madrid travel to the Basque Country with only two centre-backs in their squad: Sergio Ramos and Nacho.
Fabio Coentrao has been training alone and also misses out.
REAL MADRID SUSPENSIONS
Gareth Bale returns from a two-match ban in La Liga and the Welsh winger should start at San Mames on Saturday. Zidane has no other players suspended for the trip to Bilbao.
REAL MADRID POTENTIAL STARTING LINE-UP
Gareth Bale will be expected to return to the starting line-up alongside Cristiano Ronaldo and Karim Benzema in attack on Saturday.
Coach Zinedine Zidane is missing defenders Raphael Varane and Pepe through injury, so Sergio Ramos will be partnered by Nacho at the back.
The French coach has great options in midfield, meanwhile, but is likely to choose his favoured trio of Casemiro, Luka Modric and Toni Kroos.
ATHLETIC TEAM NEWS
Athletic Club are a strong side at San Mames, where the Basque outfit have lost just one match in La Liga all season - at home to Barcelona back in August.
Mikel San Jose is suspended, while Sabin Merino is still not ready to return despite recently recovering from injury.
BEST OPTA MATCH FACTS
Athletic Club have lost 12 of their last 14 league games against Real Madrid (winning one and drawing the other). Their only win in that time was in March 2015 (1-0 at San Mames).
Real Madrid have only won in one of their three visits to the new San Mames in La Liga (drawing one and losing the other).
Athletic Club are unbeaten in their last 13 La Liga games at San Mames (won 10, drawn three) - their best run at home since 1992 (14), when their current coach Ernesto Valverde was an Athletic player.
Cristiano Ronaldo has scored 16 goals in his 15 games against Athletic Club in La Liga, but he has failed to do so at the new San Mames (three games).
TV COVERAGE & KICK-OFF TIME
Athletic versus Real Madrid kicks off at 16:15 CET at San Mames on Saturday and cannot be shown live in the UK due to the country's broadcasting laws. However, the game will be transmitted in its entirety from 17:30 GMT on Sky Sports 5.