The visitors, meanwhile, can move two points behind their opponents in the table by securing an away victory.
Match preview
Having won all six of their opening matches in all competitions after returning from the World Cup in January, Union Berlin have hit their first slump so far this season, culminating in a disappointing 3-0 defeat to Union SG in the Europa League on Thursday.
Urs Fischer's side came from behind on three separate occasions to draw 3-3 at home in the first leg, but they had no answer for the Belgians at Lotto Park, with Janik Haberer showcasing his side's collective frustration by receiving two bookings despite only appearing as a second half substitute.
Three draws as well as a defeat to league leaders Bayern Munich in recent weeks have all but ended Die Eisernen's hopeful dreams of winning their first ever German top flight title, but Fischer will be determined not to waste their superb early season form by falling short of Champions League qualification once again.
Union Berlin were pipped by RB Leipzig in fourth by a solitary point last season, while also losing to Die Roten Bullen in the semi-finals of the DFB-Pokal. This time around, it could be Frankfurt who stand in their way of achieving on both domestic fronts, with a meeting in the quarter-finals awaiting both sides after the imminent international break.
With five points separating the two sides in fourth and sixth positions ahead of Sunday's meeting at Stadion An der Alten Forsterei, it is clearly a potentially pivotal clash in terms of shaping the top four race, with Fischer desperate for his team to get themselves back on track before the break.
Frankfurt, meanwhile, were also knocked out of Europe this week, as they succumbed to a 5-0 defeat on aggregate to Serie A leaders Napoli in the Champions League.
Oliver Glasner's side were simply outclassed by the Italians across both legs, with Victor Osimhen bagging himself a brace either side of half-time, before Piotr Zielinski dispatched a penalty after the hour mark to wrap up a comfortable 3-0 win for his team at Stadio Diego Armando Maradona.
Like their forthcoming opponents, Die Adler's attentions will now fully return to domestic matters, with Glasner and his players still hopeful of competing in Europe's elite competition once again by snatching fourth spot between now and the end of the campaign.
With only one win in their last five league games after being held at home by Stuttgart last weekend, though, their form clearly needs to improve if that is to happen. With the likes of Randal Kolo Muani in attack, they certainly have the talent on board to do so.
While Sunday's trip to the capital is not quite in the realms of the must win category yet, it is surely a match which they can not afford to lose, with eight points potentially too much of a gap to recover at this stage of the campaign.
Union Berlin Bundesliga form:
W
W
D
L
D
D
Union Berlin form (all competitions):
W
L
D
D
D
L
Eintracht Frankfurt Bundesliga form:
W
L
W
L
D
D
Eintracht Frankfurt form (all competitions):
W
L
L
D
D
L
Team News
Union Berlin's only absentee on Sunday appears to be Andras Schafer, who has been out of action for several weeks due to a foot problem.
Fischer is likely to mix things up after Thursday's defeat to Union SG, with Jordan Siebatcheu set for a recall in attack after mostly being used from the bench in recent weeks.
Christopher Trimmel and Niko Giesselmann may return to provide fresh impetus from the wing-back positions, while Haberer will expect to start in midfield despite his lack of discipline in midweek.
Frankfurt, meanwhile, will welcome their top goalscorer Kolo Muani back to their attack after the France forward missed out on the trip to Naples due to suspension after being sent off in the first leg.
Jesper Lindstrom and Eric Dina Ebimbe remain sidelined by ankle issues, while Sebastian Rode is suspended after receiving his fifth booking of the campaign against Stuttgart last weekend.
Kristijan Jakic will likely partner Djibril Sow in the visitors' engine room, with Daichi Kamada joining Mario Gotze between the lines as they look to feed Kolo Muani with chances to gobble up.
Union Berlin possible starting lineup:
Ronnow; Doekhi, Knoche, Leite; Trimmel, Laidouni, Khedira, Haberer, Giesselmann; Becker, Siebatcheu
Eintracht Frankfurt possible starting lineup:
Trapp; Tuta, Hasebe, Ndicka; Buta, Jakic, Sow, Max; Kamada, Gotze; Kolo Muani
We say: Union Berlin 1-1 Eintracht Frankfurt
Both teams have drawn each of their last two league matches, while confidence may be bruised after both crashing out of European competition during the week.
With the amount at stake in this match, it would be little surprise to see two talented teams cancel each other out to a certain extent, with both managers happy to settle on their current positions in the table.