Union Berlin must beat Union SG on Thursday to be assured of a place in the knockout stages of the Europa League.
Union Saint-Gilloise have already wrapped up top spot in Group D, but they will want to maintain their unbeaten record in the competition.
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Indeed, Union SG's first appearance in a major European competition has been a remarkable success so far, with the Belgian side taking 13 points from their five matches in Group D.
Having only ever competed in the Inter-Cities Fairs Cup - often considered the predecessor to the UEFA Cup - in the 1950's and 1960's, few would have given Union SG much chance of progressing to the knockout stages of the Europa League despite finishing second in the Belgian First Division last season.
Yet their 2-0 win away to Malmo in Sweden last week ensured that they will bypass the first knockout stage altogether and move into the last 16 having secured top spot in the group with a game to spare, even providing head coach Karel Geraerts and his players with two additional free spots in the New Year.
With league leaders Genk eight points clear of them at the top of their domestic division, Les Unionistes appear to be in a three-way fight with Royal Antwerp and Club Brugge to finish second once again, which would give them another shot at reaching the Champions League group stages having lost to Rangers in the third qualifying round in early August.
In the meantime, though, Geraerts will be desperate to make an impact in the latter stages of this competition, with owner Tony Bloom likely to be keen to see his second team remain unbeaten when Union Berlin arrive to Saint-Gilles on Thursday.
There is little doubt that Thursday's tie is a much more important one for the visitors, who will be relying on a favour from Malmo against Braga in Portugal should they fail to beat their opponents in Belgium.
Urs Fischer's side lead third-placed Braga by two points, but their identical head-to-head record (having both won 1-0 against each other on home soil) and goal difference heading into the final matchday means that a point would not be enough for the Germans to hold onto second place should Braga win as expected.
The Bundesliga leaders will be confident of amassing a fourth successive victory in the Europa League, though, having recovered from a difficult position after losing their opening two matches in the competition.
Indeed, their 2-1 victory against Borussia Monchengladbach - courtesy of Danilho Doekhi's 97th-minute winner - on Sunday kept them one point ahead of Bayern Munich at the top of the Bundesliga table, increasing their confidence ahead of a difficult trip to Belgium in midweek.
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Uion SG are likely to remain without central defender Koki Machida due to a hip injury, but otherwise Geraerts appears to have a fully-fit squad to select from.
As such, with this game essentially representing a dead rubber to his side, he could look to hand some fringe players an opportunity to impress, including exciting young talent Simon Adingra, who is on loan from Bloom's other club Brighton & Hove Albion until the end of the season.
Union Berlin, on the other hand, will almost certainly go as strong as they possibly can in terms of their starting XI, with Fischer in the enviable position of having no known injury or suspension concerns to deal with.
Doekhi could retain his place as the right-sided centre-back following his goalscoring heroics at the weekend, while club captain Christopher Trimmel may return to the side.
Union SG possible starting lineup:
Moris; Sykes, Burgess, Van Der Heyden; Francois, Puertas, El Azzouzi, Lapoussin; Amani, Adingra; Nilsson
Union Berlin possible starting lineup:
Ronnow; Doekhi, Knoche, Leite; Trimmel, Schafer, Khedira, Haberer, Ryerson; Becker, Siebatcheu
We say: Union SG 0-1 Union Berlin
With Union SG having very little to play for in this match, we can envisage Union Berlin edging a tight encounter on Thursday to progress to the knockout stages alongside their opponents.
Fischer's side have scored three goals and only conceded twice in five European matches this season, so the Bundesliga leaders clearly possess the know-how to grind out results.
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