The hosts are 10th with 16 points after 11 matches and were beaten 1-0 by Wolfsburg on November 23, while Leverkusen are only in fourth place with 20 points but did triumph 5-2 against Heidenheim last Saturday.
Match preview
Union Berlin created no big chances against Wolfsburg and were restricted to just 0.51 xG, though to their credit they at least limited the Wolves to one big chance.
Boss Bo Svensson was scathing of his players following the defeat but suggested that they could have earned a point, saying: "We were too passive and lacked courage and good sequences of play in attack. It got better in the second half, partly due to the substitutions, and I think it was more of a draw in the end."
Svensson's side have had contrasting fortunes at either end of the pitch given they have only conceded nine goals but have only scored nine times in the Bundesliga, records which make them the division's joint second best defensive and second worst offensive club.
Die Eisernen are in poor form having lost three and drawn two of their five most recent fixtures, failing to find the back of the net in their last four.
It should be noted that the hosts have still been difficult to beat at home, with the team so far unbeaten at Stadion An der Alten Forsterei in 2024-25, winning three and drawing two.
As for Leverkusen, while their nine-point deficit on leaders Bayern Munich is by no means unrecoverable, fans will no doubt be concerned that the club have already dropped points six times this season.
In fact, the visitors only failed to win in the league on six occasions in the entirety of the 2023-24 campaign, and despite having 23 matchweeks left to play this term, Alonso's side are unable to equal their points tally of 90 from the previous season.
However, Die Schwarzroten's victory against Heidenheim at least ended a streak of three consecutive Bundesliga draws, and saw them score as many goals in one game as they had in the prior four top-flight outings.
Leverkusen also managed to beat RB Salzburg 5-0 on Tuesday in the Champions League, with the team now sixth in the Champions League table with 10 points after five fixtures.
Alonso's team have emerged victorious in two of their last five games, drawing two of the other three, while scoring 11 times in their most recent three.
Though Die Schwarzroten have struggled for consistency this term, they have at least been difficult to beat away from home given they have drawn four and lost just one of their past five matches on the road.
Union Berlin Bundesliga form:
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Union Berlin form (all competitions):
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Bayer Leverkusen Bundesliga form:
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Bayer Leverkusen form (all competitions):
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Team News
Union Berlin have three injury concerns heading into Saturday's clash, with striker Andrej Ilic, centre-back Diogo Leite and goalkeeper Yannic Stein all ruled out.
Federik Ronnow is certain to start between the posts, while Danilho Doekhi, Kevin Vogt and Leopold Querfeld could be selected to play in a back three.
Given Ilic's absence, Svensson may field a front three featuring Woo-Yeong Jeong, Jordan Siebatcheu and Benedict Hollerbach.
Opponents Leverkusen will not be able to select attackers Amine Adli, Victor Boniface, Jonas Hofmann and Martin Terrier, and this could force Alonso to start just two forwards.
Florian Wirtz and Patrik Schick can be expected to feature up front, while Granit Xhaka, Robert Andrich and Aleix Garcia may start in midfield.
Defenders Jeanuel Belocian and Nordi Mukiele will also not appear in the starting XI, and this could mean that the visitors deploy a back three consisting of regulars Edmond Tapsoba, Jonathan Tah and Piero Hincapie.
Union Berlin possible starting lineup:
Ronnow; Doekhi, Vogt, Querfeld; Trimmel, Kemlein, Khedira, Rothe; Jeong, Siebatcheu, Hollerbach
Bayer Leverkusen possible starting lineup:
Hradecky; Tapsoba, Tah, Hincapie; Frimpong, Xhaka, Andrich, Garcia, Grimaldo; Wirtz, Schick
We say: Union Berlin 1-2 Bayer Leverkusen
Following their resounding victory in the Champions League, Leverkusen will come into Saturday's match full of confidence.