Carlo Ancelotti's men are yet to concede a goal in 2014 but face a tough test against a side that have not lost a single game on home soil in La Liga this season
Carlo Ancelotti's side may be chasing down a four-point deficit by the time their game at San Mames gets under way, with La Liga's co-leaders, Barcelona and Atletico Madrid, both in action before Los Blancos.
The Blaugrana host Valencia on Saturday, while the Rojiblancos face Real Sociedad at the Vicente Calderon just hours before Madrid take to the field in Basque country.
The Santiago Bernabeu side have been in exceptional form recently, with their last defeat in any competition coming against Barca at Camp Nou on October 26.
They have won 17 of their 20 matches since then, a run that has seen them reach the Copa del Rey semi-finals and the last 16 of the Champions League.
Forwards Cristiano Ronaldo and Karim Benzema have helped Madrid become the most prolific side in the Spanish top flight, with 60 goals this term.
Welshman Gareth Bale has also chipped in with eight goals from 14 league appearances, but he could miss the trip to Bilbao with a leg injury.
Los Blancos, though, have won all eight of their matches so far this year without conceding a goal, making this their best January ever.
However, they face an Athletic outfit with an imposing home record, with Ernesto Valverde's side yet to lose a match at San Mames in La Liga this season.
And although they lost in the Copa del Rey to Atletico Madrid on Wednesday, bowing out 3-1 on aggregate, they have won their last three league matches, scoring freely in the process.
A 6-1 thrashing of Almeria on January 11 was followed by 4-2 and 5-1 successes against Real Valladolid and Osasuna, respectively.
History is on Madrid's side, though, with the capital club having won the last eight meetings between the two teams in comfortable fashion, scoring at least three goals in all of their triumphs.
An Isco double helped Real to a 3-1 win in the match earlier this season, while Ronaldo also scored in the home triumph.
In terms of team news, centre-back Raphael Varane is back in training for the visitors following a knee problem, but is yet to return to first-team action.