Los Blancos are currently four points clear of second-placed Barcelona at the summit, while Athletic occupy eighth position, just four points off sixth-placed Getafe in the race for a Europa League spot.
Athletic have been in impressive form since returning to action after the lockdown period, winning three, drawing two and losing just one of their six matches in Spain's top flight.
The Basque outfit have won three of their last four in the league, including an impressive 2-0 success at Valencia on Wednesday night, with their only defeat since during the same run coming against Barca.
Gaizka Garitano's side are currently eighth in the table, just four points off sixth-placed Getafe, who appear to be battling Villarreal, Sevilla and Atletico Madrid for two Champions League spots.
Athletic have been impressive on home soil in the league this season, winning nine of their 16 matches, which is a record only bettered by Atletico Madrid, Real Madrid and Barca.
They have not beaten Los Blancos in La Liga since March 2015, although four of the last five meetings between the two sides in Spain's top flight have finished level.
Zinedine Zidane's side have now beaten Eibar, Valencia, Real Sociedad, Mallorca, Espanyol and Getafe since returning to action last month, which has seen them move to the top of the table.
The gap to second-placed Barca is currently four points, but the reigning champions do not face Villarreal until Sunday night, meaning that Madrid will have the chance to open up a seven-point advantage when they take to the field against Athletic on Sunday afternoon.
It is difficult to see where Los Blancos are going to drop points as they face Alaves, Granada, Villarreal and Leganes in their final four matches of the season.
Much of the team's success domestically this term has been built on a strong defence, with Zidane's team conceding just 21 times in their 33 matches, which is comfortably the best record in the division.
Athletic Bilbao La Liga form: DDWLWW
Real Madrid La Liga form: WWWWWW
Athletic will again be without the services of experienced midfielder Benat due to a hip problem, but the home side are otherwise in good shape when it comes to injuries.
As for Madrid, key centre-back Raphael Varane is a doubt with a head injury after being forced off against Getafe on Thursday night when he was hit in the face by the ball.
Los Blancos will allegedly not make a final decision on the Frenchman until the morning of the match, although various reports in Spain have suggested that he will be available.
Nacho is still on the sidelines through injury, but Eden Hazard was only rested against Getafe and is likely to return to the starting XI for this match, potentially joining Karim Benzema and Isco in attack.
Zidane also has a decision to make when it comes to his midfield, and there is a chance that Federico Valverde's energy could be preferred to Luka Modric's experience alongside Casemiro and Toni Kroos.
Athletic Bilbao possible starting lineup:
Simon; Capa, Yeray, Martinez, Yuri; Lopez, D Garcia; Muniain, R Garcia, Cordoba; Williams
Real Madrid possible starting lineup:
Courtois; Carvajal, Varane, Ramos, Mendy; Kroos, Casemiro, Valverde; Hazard, Benzema, Isco
We say: Athletic Bilbao 1-1 Real Madrid
As mentioned, four of the last five La Liga meetings between these two sides have finished level, while Madrid have not won at San Mames in the league since March 2017. Los Blancos are on a roll at the moment, but Athletic are also in impressive form, and we fancy a low-scoring draw on Sunday night.