The Basque club, fiercely proud of their heritage and always keen to thwart their detested rivals from the capital, are fourth, largely thanks to their record at home where they have won 11 and drawn two in front of their passionate supporters.
They are the only team who have beaten champions Barca, a 1-0 success at the San Mames at the beginning of December, and Real's task may be made even harder as Bilbao will still be smarting after being dumped out of the Copa del Rey by Atletico on Wednesday.
Carlo Ancelotti's Real side have not been tested since they needed a late winner to secure a 3-2 victory at Valencia at the end of December but another victory on Sunday would be a big fillip as they head towards a key stage of the season in La Liga, the cup and the Champions League.
Defeat could see them fall four points behind in the title race and burst the bubble of optimism that has grown around the club in recent weeks.
"It's very important," Ancelotti told a news conference on Tuesday after Real's 1-0 win at home to Espanyol secured their place in the Cup semi-finals.
"It's a tricky match because Athletic are playing very well at the moment and everyone knows playing at the San Mames is not easy," added the Italian, in his first season in charge since taking over from Jose Mourinho.
"But it's a good time for us to be playing there. We have confidence and desire and we are excited about giving everything to win."
Ancelotti may be without record signing Gareth Bale for the trip north.
The Wales winger, whose first season in Spain has been disrupted by minor injuries, had to come off at halftime in last weekend's 2-0 win at home to Granada due to a problem with his left leg and missed the cup game against Espanyol.
Ancelotti said if Bale was unavailable, forward Jese would likely be deployed up front alongside regulars Cristiano Ronaldo, the FIFA Ballon d'Or winner and La Liga top scorer with 22 goals, and Karim Benzema.
Barca and Atletico, who top the table on 54 points from 21 matches, with Real a point back at third, also have potentially tricky games this weekend, with Barca hosting mid-table Valencia on Saturday and Atletico at home to sixth-placed Real Sociedad on Sunday.
The joint leaders returned to winning ways last weekend after consecutive draws, including a 0-0 stalemate between the pair at Atletico's Calderon stadium.
OPTA HEAD-TO-HEAD STATS
OPTA MATCH FACTS
- Athletic have lost eight consecutive league meetings with Real Madrid; only once before have they endured a longer run against their rivals (10, between 1959 and 1964).
- The Whites have won their last three trips to Bilbao in La Liga by the same scoreline: 3-0.
- The side from Bilbao are just three points away from equalling their overall points haul from the 2012/13 campaign (45).
- The Lions have collected three consecutive league wins; they have not won four in a row since February 2011.
- Real Madrid have kept four successive La Liga clean sheets; they have not kept more since a run of six under Bernd Schuster in 2008.
- If they avoid defeat here, Carlo Ancelotti’s Real Madrid will have beaten Jose Mourinho’s side’s run of 20 consecutive games unbeaten in all competitions from 2011/12 (20).
- Cristiano Ronaldo has had more shots (158) and shots on target (64) than any other player in the top five European leagues this term.
- Gorka Iraizoz, together with now-teammate Diego Lopez, has conceded more goals to Cristiano Ronaldo than any other La Liga goalkeeper (11).
- Aduriz (three goals, four assists) and Ibai Gomez (five goals) have participated in 10 of Athletic’s last 12 league goals.
- The Basque side have recouped a league-high 18 points from games in which they have conceded the first goal this term (14), while Real Madrid have not lost a single point having scored first.
EUROPEAN GAMES COVERED LIVE ON EUROSPORT-YAHOO! THIS WEEKEND
- Sports & Recreation
- Real Madrid
- Atletico Madrid
- Athletic Bilbao
- La Liga
- Carlo Ancelotti
- Cristiano Ronaldo