The hosts advanced to the third round of the DFB-Pokal with a 3-0 win over Hannover 96 just before Christmas, whereas Union Berlin exited the competition with a 3-2 defeat to Paderborn.
Werder Bremen are regarded as one of the giants of the German game, but they are edging closer towards a second relegation dogfight in as many seasons following a string of poor results.
Florian Kohfeldt's side suffered four defeats on the trot to Wolfsburg, Stuttgart, RB Leipzig and Borussia Dortmund but did manage to end their losing streak with a hard-fought 1-0 win over 17th-placed Mainz 05 in their most recent Bundesliga outing.
The only goal in that game came from an unlikely source in Eren Dinkci, who came off the bench to score on his debut for the club after a prolific run for the second team.
The 19-year-old had only been on the pitch for five minutes before heading in a last-minute winner for 13th-placed Werder Bremen, who ended a nine-game winless run in the German top flight with only their second away league victory of the campaign.
Kohfeldt's men followed up their nervy win over Mainz with a resounding 3-0 triumph over Hannover 96 in the second round of the DFB-Pokal, with Jean-Manuel Mbom, Josh Sargent and Theodor Gebre Selassie chalking up the goals in that victory.
If 2021 is anything like 2020 was for Union Berlin, the Eisernen faithful have plenty to look forward to from their side in the second half of the season.
Urs Fischer's men cemented their status as a Bundesliga club last season and have already produced plenty of impressive results in the current campaign - including a 2-1 triumph over Borussia Dortmund in their last top-flight outing before Christmas.
This weekend's visitors have only suffered two Bundesliga defeats all season and deservedly occupy a spot in the top six ahead of their first match of the New Year, but Stuttgart and Borussia Monchengladbach are only three points behind and ready to pounce on any slip-ups.
However, something has to give when fourth-placed Wolfsburg play fifth-placed Dortmund on Sunday, so Union Berlin can temporarily rise to fourth and likely end the weekend in fifth should they take the spoils at Werder Bremen, whom they beat 2-0 in this fixture last season.
Despite holding their own in the top flight, Union Berlin's DFB-Pokal journey ended prematurely as second-tier side Paderborn won 3-2 in the second round on December 22, which was only their second defeat in 13 matches across all competitions.
Werder Bremen Bundesliga form: DLLLLW
Werder Bremen form (all competitions): LLLLWW
Union Berlin Bundesliga form: WDLDDW
Union Berlin form (all competitions): DLDDWL
Werder Bremen's only long-term injury concern at the minute is Milot Rashica, who is yet to recover from the hamstring problem that kept him out of action in December.
However, fellow forward Niclas Fullkrug is back in training and could play a part at the weekend, although Dinkci is unlikely to be rewarded with a start despite his heroics against Mainz.
Union Berlin star man Max Kruse, who already boasts six goals in the league this season, will play no part against his former club as he nurses a thigh problem.
Werder Bremen possible starting lineup:
Pavlenka; Toprak, Friedl, Gross; Gebre Selassie, Eggestein, Mohwald, Augustinsson; Bittencourt, Osako; Sargent
Union Berlin possible starting lineup:
Luthe; Trimmel, Knoche, Friedrich, Lenz; Griesbeck, Andrich; Becker, Promel, Bulter; Awoniyi
We say: Werder Bremen 1-2 Union Berlin
Having already overcome Dortmund and held Bayern Munich to a draw this season, Union Berlin will certainly feel capable of taking all three points in this one. Werder Bremen will be buoyed by two positive results and should be able to welcome a few attackers back from injury, so the hosts should have no problem getting on the scoresheet, but we are still expecting a narrow away win.