Anoeta has been a difficult venue for the Blaugrana in recent years, but Ernesto Valverde's side travel to San Sebastian unbeaten in the Primera Division and nine points clear of Atletico, with Real Madrid provisionally 14 adrift with a game in hand.
Here, Goal takes a look at everything you need to know ahead of the Catalans' trip to the Basque Country...
Defender Samuel Umtiti is still sidelined, while striker Paco Alcacer is doubtful for the game at Anoeta.
Recent signing Philippe Coutinho is out for around 20 days with a minor injury and will have to wait for his debut.
Sergio Busquets was suspended for the 3-0 win against Levante last weekend after picking up his fifth booking of the league season in the Clasico victory over Real Madrid before Christmas, but the midfielder returns on Sunday and coach Valverde has no other players banned for the game in San Sebastian.
BARCELONA POTENTIAL STARTING LINE-UP
Busquets will return to the starting line-up after missing the win against Levante last weekend through suspension.
Also in midfield, summer signing Ousmane Dembele is set to feature on the right once again, with Luis Suarez and Lionel Messi further forward.
And in central defence, Valverde is likely to recall Thomas Vermaelen after Javier Mascherano played in the 5-0 win over Celta in the Copa del Rey on Thursday.
Yerry Mina, who was signed from Palmeiras this week for €11.8m, is likely to have to wait for his debut, as will the injured Coutinho.
REAL SOCIEDAD TEAM NEWS
Real Sociedad beat Sevilla 3-1 in their last Liga game at home, but lost 1-0 to Leganes in the 18th round of matches and coach Eusebio (a former Barca midfielder) admits he is under pressure if results do not improve soon.
The Basques are in 12th place after 18 games, with just 23 points (not even half of Barca's total of 48), although they are only five behind Villarreal in sixth.
TV COVERAGE & KICK-OFF TIME
Real Sociedad versus Barcelona kicks off at 20:45 local time at Anoeta on Sunday and will be broadcast live in the UK on Sky Sports Football from 19:40 GMT.
In the United States, the game can be watched live on television on beIN Sports and kicks off at 14:45 ET.
BEST OPTA MATCH FACTS
Real Sociedad are unbeaten in their last seven La Liga games at home against Barcelona (won five, drawn two). Their last defeat at Anoeta against the Blaugrana in this competition was a 2-0 loss in May 2007.
Those seven games without a win mark Barcelona’s worst streak as a visitor in La Liga this century.
Barcelona are already winter champions with 48 points from their opening 18 games of the season. In 11 of the last 13 seasons that they have led at this stage, the Blaugrana have gone on to win the title (Atletico in 2013-14 and Real Madrid in 2006-07 are the exceptions).
Lionel Messi has scored 14 goals in his 19 games against Real Sociedad in all competitions, but only four of them at Anoeta.
The two La Liga players who have provided the most assists to a single team-mate this season are Jordi Alba to Messi and Sergi Roberto to Luis Suarez (with five each).