The Bundesliga side suffered a 1-0 defeat to Real Madrid in their first game in Group C last time out, while Braga suffered a 2-1 home loss to Italian giants Napoli.
Match preview
Union Berlin's first-ever Champions League campaign ended in late heartbreak, as Jude Bellingham scored a last-gasp winner for Real Madrid in the contest in the Spanish capital.
The Iron Ones finished fourth in the Bundesliga last season to secure a position in this competition for the first time in their history, and they will have been pleased with their performance in Madrid last time out, but the team's recent form is a huge concern ahead of this contest.
Indeed, Urs Fischer's side have lost each of their last five games in all competitions, including their last four in the Bundesliga, with Saturday's 1-0 defeat to Heidenheim leaving them down in 11th spot in the table on six points.
The German side will be aware of the importance of the games against Braga in this section, as they will surely need to win both to stand a chance of advancing to the next round due to the strength of Real Madrid and Napoli.
Union Berlin actually locked horns with Braga in last season's Europa League group stage, with both teams recording 1-0 home victories in the section.
Braga were also close to securing what would have been a welcome point in their opening match in Group C, with Bruma levelling against Napoli in the 84th minute of their contest in Portugal.
However, an own goal from Sikou Niakate handed the Italians a 2-1 victory in the final exchanges, leaving Braga third in the section on zero points, with these two teams already playing catch-up in the group.
Artur Jorge's side will enter this match off the back of a 4-2 victory over Estrela in the league, and they currently sit fifth in the Primeira Liga table, boasting 13 points from their opening seven matches.
Os Arcebispos were last present in the group stage of the Champions League in 2012-13, finishing fourth in a section which included Manchester United.
Braga also failed to make an impression in either the Europa League or Europa Conference League last season, so it would be a shock if they were able to advance through this section, but the team will have gained plenty of confidence from their performance against Napoli.
Union Berlin Champions League form:
L
Union Berlin form (all competitions):
W
L
L
L
L
L
Braga Champions League form:
W
W
W
W
L
Braga form (all competitions):
D
W
L
L
W
W
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Team News
Union Berlin will be without the services of four first-team players for this match, with Robin Knoche, Laurenz Dehl, Andras Schafer and Rani Khedira currently on the sidelines.
Kevin Behrens has been the team's main source of goals this season, netting four times in all competitions, and he will again operate in the final third of the field for the home side here.
Head coach Fischer will make changes from the side that started in the league last time out, with Aissa Laidouni and Josip Juranovic set to be brought back into the XI.
Braga, meanwhile, have close to a fully-fit squad for this match, with the only exception being Victor Gomez, who was forced off after five minutes of their league game on Thursday night.
Alvaro Djalo is the team's leading goalscorer this season with six, and he is again expected to feature in the starting side, while Bruma, who has five goals this term, will also be in the XI.
Ricardo Horta is another player to come up with five goals in all competitions this season, and the 29-year-old is set to operate as the number 10 behind Abel Ruiz on Friday night.
Union Berlin possible starting lineup:
Ronnow; Doekhi, Bonucci, Leite; Juranovic, Kral, Tousart, Laidouni, Gosens; Becker, Behrens
Braga possible starting lineup:
Matheus; Oliveira, Fonte, Niakate, Borja; Carvalho, Al Musrati; Djalo, Horta, Bruma; Ruiz
We say: Union Berlin 1-2 Braga
Union Berlin are in need of a big result to act as a springboard amid their disappointing form, but we are finding it very difficult to back them at the moment. Braga are full of quality in the final third of the field, and we are expecting the Portuguese side to claim all three points on Tuesday night.