The Portuguese outfit have lost both games against Red Bull Salzburg and Inter Milan, while the La Liga outfit secured maximum points in Austria on matchday two.
Match preview
Benfica were tipped to go through in their Champions League group after the draw, but Roger Schmidt's team are bottom heading into matchday three.
The Eagles were stunned by 10-man Salzburg in Portugal on matchday one before losing at San Siro, leaving them playing catch-up before facing the Spanish outfit.
With four points separating both sides, the defending Primeira Liga champions could reduce the deficit to one with a victory and hope Inter claim maximum points against Salzburg in the other fixture in Group D on Tuesday.
Benfica lost an eight-game unbeaten group stage run against the Austrian side, and a 10-game undefeated away run in Europe was halted by the Nerazzurri last time out; the Eagles hope to show something different to get points on the board on matchday three.
Having scored four times in a 4-1 win against Lusitania in Taca de Portugal action on Friday, Schmidt will hope his team are similarly clinical against Sociedad.
The La Liga side will not be compliant opponents, buoyed by a 2-0 victory over Salzburg last time out.
La Real had Mikel Oyarzabal and Brais Mendez's goals in the opening 30 minutes to thank for the early advantage, and they held on until the final whistle.
That triumph was Sociedad's first Champions League group-stage victory since defeating Galatasaray in September 2003 (they got one point from 18 in the 2013-14 group phase), leaving Imanol Alguacil's side joint-top with Inter after two games.
The San Sebastian side travel to Lisbon looking to continue their unbeaten run in this season's competition, but they must prepare for a barrage from a motivated side backed by the home support at Estadio da Luz.
While the unconvincing 1-0 victory over Real Mallorca on Saturday does little for optimism, La Real's ambition to progress from Group D should fuel them at Benfica.
Benfica Champions League form:
L
L
Benfica form (all competitions):
L
W
W
L
W
W
Real Sociedad Champions League form:
D
W
Real Sociedad form (all competitions):
W
W
W
W
L
W
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Team News
Angel Di Maria and Alexander Bah do not return from their injuries until November, meaning Schmidt must make do without a potential match-winner and key defender.
Fredrik Aursnes could be trusted at right-back to replace Bah, with Benfica expected to line up in a 4-2-3-1.
Sociedad have a few doubts, as Andre Silva, Alvaro Odriozola and Kieran Tierney are touch-and-go due to muscle issues.
Martin Merquelanz is undoubtedly ruled out with a knee injury for La Real, who should continue with their 4-4-2 in Lisbon.
Benfica possible starting lineup:
Trubin; Aursnes, Silva, Otamendi, Bernat; Neves, Kokcu; Neres, Silva, Marlo; Musa
Real Sociedad possible starting lineup:
Remiro; Traore, Zubeldia, Le Normand, Munoz; Mendez, Merino, Zubimendi, Barrenetxea; Oyarzabal, Fernandez
We say: Benfica 2-1 Real Sociedad
With Benfica's situation in Group D almost precarious, the Portuguese giants should eke out a victory over Sociedad to close the gap on the current joint-leaders to one.